...there is dead space ventilation in the device that seems greater than in the standard snorkel tube. That dead space can cause carbon dioxide buildup." This CO2 buildup could cause a person to become disoriented, or, even lose consciousness.
...she had negative pressure pulmonary edema, which is caused by an upper airway obstruction generating enough pressure to pull fluid from the arteries that take blood to the lungs.
Snorkelling safety: Snorkelling is a simple and fun activity for all the family! Breathing through a snorkel is more physically demanding than regular swimming. If you feel tired, short of breath or dizzy, remove your mask and get out of the water. Do not use this product if you have cardiovascular or respiratory problems (chest infection, angina, asthma, high blood pressure, heart disease, etc.). If in doubt, consult your doctor.
Pietro es un chico de ciudad, Bruno es el último niño de una localidad de montaña olvidada. Con el paso de los años, Bruno se mantiene fiel a su montaña, mientras que Pietro viene y va. Sus experiencias le harán enfrentarse al amor y a la pérdida, recordándoles sus orígenes y abriendo paso al destino.
With
this information in mind, I set my GF low to roughly counteract the
ZH-L16 “b” parameters (I have been using Shearwater dive computers with
ZH-L16 GF in conjunction with my tried and true decompression tables for
about three years). In ZH-L16, the average of “b” parameters is 0.83. I choose my GF low to be about 83% of the GF high, for instance GF 70/85.
Although the algebra is not exact, this roughly counteracts the slope
of the “b” values. This approach allows me to believe I have chosen my
GF rationally, is not so large a GF low as I am unable to convince my
buddies to use it, and satisfies my preference to follow a relatively
shallow stops schedule.
The subsequent decompression profile that is generated on the ascent should not exceed the tolerated over-pressure value, or M value — a theoretical construct for the theoretical controlling tissue compartment within the body, in order to avoid decompression illness (DCI). As each compartment comes into play and the relevant M value is reached, a decompression stop profile is generated.
Figure 1 represents a very simplistic example involving just one of the fast tissues which will control the primary ascent phase. The M value for this compartment is shown as a straight line. If the diver controls the ascent, the inert gas loading in the compartment will stay on or below the M value line. If they do this, let’s assume they are using 100% of the available M value, which means there’s no extra safety margin for that dive; they are theoretically diving right on the edge of the model.
For a typical bounce dive, Buhlmann standard practice has been to allow a rapid ascent to the first stop to generate a high level of off-gassing. Doing this, the gas loading in the fastest compartment will be on or near saturation at the bottom depth (the slow tissues are only partially saturated). This means that the fastest compartments will control the initial ascent since their gas loadings will be near or on the tolerated over-pressure value (M value). The first stop depth is set when the controlling (fast) compartment is nearest to the M value. The example only shows up to a point where the first stop starts and does not detail the other compartments or the remaining decompression.
Using gradient factor terminology, the M value line is the 100/100 reference. The first 100 describes how close (in percentage) to the M value line the first stop is, and the second 100 describes how close the final stop is. Thus 100/100 has no added safety margin compared to the M value. In the complete picture, each compartments’ M value and each compartments’ internal pressure right through to the end of the dive (not just to the stop as drawn) would be displayed on the graph each with the same 100/100 gradient. The slower compartments would reach their M value during the final decompression phases while the faster compartments control the deeper decompression.
The gradient factor system modifies the M value by taking a percentage of the difference between the M value and the ambient pressure value. As a simple example to illustrate how Gradient factors work, using 80% of the M value as the controlling value (80/80 line) produces a line on the graph (figure 2) below the 100/100 line, having the effect of reducing the compartments allowed over-pressure value and generating a deeper decompression stop.
Again, in the complete picture all the adjusted M values and compartment pressures would be plotted, adding safety to the whole decompression profile.
As most of these early dissolved gas based tables were formulated around relatively shallow water air range dives, they do not suit deep water dives, although historically they have often been extrapolated for use in deep-water. While these tables have a varying solution for different depths they were depth limited.
So what about Pyle stops? Technical diving pioneer, ichthyologist Richard Pyle developed a practical solution that divers could understand for modifying the decompression profile to reduce the excessive over-pressurization of the controlling compartment at the deep stops. He found that by stopping and venting a fish’s swim bladder below the first tabular stop depth, he ‘felt better’ at the end of the decompression. He was in effect allowing the faster compartments’ pressure to reduce before ascending to the tabular first stop and not reach its M value peak.
The downside of this was that other compartments were still on-loading gas, which could generate an additional decompression obligation in shallow water. He was applying a safety factor that only had an effect on the deeper stops. This had the potential to allow the slower compartments to become closer to their M value during the shallow water decompression phase unless additional safety factors were applied.
Gradient factors can further mimic bubble models by using two different gradient factors to control the decompression: one that primarily references the deep stops, and one the shallow.
So a 20/80 gradient factor, which has been commonly used on deeper dives, would allow an over-pressure value of 20% (instead of 100%) of the difference between the ambient pressure and the allowed M value for the controlling compartment of the first or “deep stop” and 80% (instead of 100%) of the M value for the controlling compartments’ pressure difference at the shallow stop. The stops in between are calculated by drawing an over-pressure value line between the two points and plotting the new adjusted M values for each compartment in between. It assumes a linear calculation between the adjusted first and last M values.
In Figure 3 let’s assume that compartment 4 controls the deep stop and compartment 16 the shallow stop. Again, for clarity, the on-going compartment inert gas loading reductions are not shown past the M value point, neither are all the other compartment M values.
The major drawback of gradient factors is that the factors applied need to be adjusted for each depth/time exposure. For example, if you used the same 20/80 gradient factor for an 80 m dive, on a 30 m dive you might have an excess of decompression in shallow water because we know from experience that a gradient factor of close to 100/100 is reliable for this shallow water dive.
What does this mean? First, it is not necessarily appropriate to apply one gradient factor to a range of dive depths. What works deep may not work shallow. Secondly, it means just applying gradient factors in the first place may be too coarse a solution. Just drawing a straight line between the M value points and assuming the mid-water decompression follows this linear approach may not work. So how do we generate a refinement?
Stochastic modelling has been around in diving for some time. Decompression tables are generated based on statistical dive data of incidents; basically, points are plotted on a graph and an algorithm generated. So how could we use this to improve gradient factor modelling? Assuming the 100/100 factor is OK for a certain shallow dive and the 20/80 is OK for a particular deep dive, would it not be best to have a varying gradient factor depending on depth/time exposure and other factors? If we can be fairly certain of key decompression times for a range of depth/time exposures that are ‘safe’ and generate reasonable decompressions, we could use them to generate a gradient factor that varies accordingly. My term for this approach is a Variable Gradient Model (VGM).
A better alternative to fooling the decompression algorithm is to limit the severity of the exposure while fully informing the model. This brings us back to gradient factors, which are defined by two values: The first number of the pair (“GF low”) represents the percentage of the M-value that establishes the first stop during ascent; the second number (“GF high”) is the percentage of the M-value that should not be exceeded at any point during surfacing. The dive computer effectively draws a straight line between the two, creating the ascent slope.
De cara a personalizar el modo Recreativo, cambiar los límites de alertas de presión de botella y sustituir alguna de la info por defecto por otra más relevante.
Actualización a 29/05/2023: Pos, por ahora, simplemente he cambiado del Layout Big al Normal.
Version 17 includes the following changes: -Fixes issue where under some conditions units may not shutoff when left on charger. -Fixed issue where surface interval was logged and displayed incorrectly when greater -than 45 days. -O2 % threshold for considering a gas a “deco gas” now 40% O2 (previously 50%). -SAC calculations for display in dive log modified slightly to match the Perdix AI. -Adds “EN250” information to dive mode start screen for some models.
Version 18 includes the following changes: -Fixes issue that could cause a Watchdog Reset error in certain circumstances. -Fixed error where in CC/BO the dive log gas lists were swapped. -O2 % threshold for considering a gas a “deco gas” now 40% O2 (previously 50%). -Fixed display error in menu where in Gauge mode the GTR/SAC option value displayed as “Off (Gauge) Off” instead of just “Off (Gauge)”.
Version 19 on the Teric includes the following changes: -Up to 4 wireless air integration (AI) tanks are now supported -A sidemount mode has been added -AI tanks can now be renamed. Only 2 characters available per tank -Gas density display is now available -Additional power management options have been added.
Version 21 includes the following change: -This version addresses a minor bug where the Swift AI Tank Pressure Transmitter will occasionally send a false and unwarranted low battery warning. This change suppresses AI transmitter low battery warnings until four (4) have been received consecutively.
Version 23 includes the following change: -Fixed display issue with Air Integration (AI) info row when the only AI Transmitter enabled was T4, the T3 transmitter would erroneously display instead. -Fixed issue where the AI serial number was saved with wrong byte ordering in the dive log.
Imagine having a tool that would give you a numerical percentage value of the decompression stress you would encounter if you were to instantaneously ascend to the surface. Not all dives are created equal. You might be keeping your dives within the NDL, doing your safety stops, but the fact is that different NDL dives will give you different degrees of DCS stress depending on your dive profile. When we launched the Teric we included in it a new feature we called Surface GF (SurfGF). In this blog post we'll discuss SurfGF and how it can help you manage your decompression stress.
...
Setting your conservatism levels in this mode can be as simple as selecting from 3 settings: Low, Medium or High. There is a fourth setting called Custom. We recommend that divers refrain from tweaking the custom settings until the diver is familiarized with Gradient Factors (GF). Once you have grown to be knowledgeable about GF, then you can access conservatism levels that range from 10 to 99 in GF Low (90 settings) and from 30 to 99 in GF High (70 settings).
...
What is GF? Erik Baker developed gradient factors as a conservatism strategy. It is often used in conjunction with the Buhlmann ZHL-16 algorithm. This conservatism strategy provides divers with a good amount of flexibility that allows us to fine tune our dive profiles and how we address DCS risk during a dive. One of its virtues is that it allows users to implement varying degrees of deep stops – how deep do you want to start your stops – through the GF Low parameter. At the same time, by adjusting the GF High parameter you decide how long your shallower stops will be. Both the Buhlmann ZHL- 16 and the Gradient Factors conservatism strategy are open source and readily available to divers for in depth study in relation to their individual responses to decompression stress. This is one of the reasons that has made it so popular with divers, which in turn has yielded a good amount of empirical validation for divers and earned their trust.
...
facing a forced ascent when your SurfGF says 73% is a much different scenario than facing a SurfGF of 187%. The higher the percentage, the more likely you are to getting bent. Any percentage above 100% carries a risk higher than surfacing at the Bulhmann M-value itself (GF 100% = M-Value).
...
Making a mental note of your SurfGF at the time you arrive at the surface can also provide valuable information. Sometimes after a dive you can feel more tired than usual. Is it DCS stress? It would help if you have a numerical value to associate that feeling with.
...
SurfGF can give you valuable information when facing difficult choices. It is better to be bent than drowned. Sometimes breaking a deco stop is the safer choice. Shearwater won’t lock you out for doing that. SurfGF will give you a number that can influence a tough decision on whether to head to surface during some urgency or do some more deco. When used along with GF99 you can numerically manage your deco stress all throughout the entire dive. GF99 tells you the gradient factor as a percentage for your current depth and time. SurfGF is also useful for dives within the NDL. You can objectively see the effects of doing a 3 minute safety stop and compare it to a 5 minute safety stop or even to having no safety stop at all. If you have a strenuous dive doing heavy kicking while battling a current, you can consciously choose to surface at a SurfGF of 70% instead of your usual 85% just to pad your chances. Now you can apply numerical values to your padding. Please bear in mind that while SurfGF is a powerful tool it is not a replacement for proper dive planning. You can program your Teric to have the SurfGF value to appear in your home screen and always be present during the dive without needing to touch a button. After divers discovered SurfGF on the Teric and the word spread around, we got many requests to add this feature to our other computers. So we did.
Vale, y habla de usar un GF99 de entre 1/3 y 1/2 del GF Hi para maximizar la desaturación:
In contrast, you can use the GF99 display to ascend to a depth that guarantees more efficient nitrogen removal. As a rule-of-thumb, you should aim for anywhere between 1/3 and 1/2 of your preset GFhi. For instance, if your GFhi is set at 85%, aim to conduct your safety stop at a depth that creates a GF99 between 28% and 42%.
Sobre la velocidad de ascenso:
I will always ascend at 9-10m per minute from the bottom to my safety stop. Then, from the safety stop to the surface, I will ascend at a rate of 3m per minute. This strategy works very well for avoiding post-dive fatigue.
Actualización a 04/06/2023: Biosnar:
Actualización a 08/06/2023: Correa en casa y montada:
Definitivamente, tenía que haberla pillado en 22 y no en 20. Me dí cuenta luego. Voy a probarla y decidir si así o como la venden.
Actualización a 10/06/2023: Acabo de personalizar ya que no encontraba el GF Surface durante las inmersiones y tenía que andar cambiando al GF99 para hacerme una idea de cómo tábamos limpiando en los ascensos.
Así:
Actualización a 17/06/2023: Hoy lo he usado en Técnico:
MÁS deco. :P
Actualización a 21/06/2023: Pantalla de Técnico por defecto:
Personalizada:
P.D: Info:
Nota: Todavía no lo he vuelto a cargar.
Actualización a 26/06/2023: Sigo en Técnico y he cambiado la personalización de la pantalla para no tener el NDL duplicado (ya que va en la de Deco) y mostrar el GF Surface (bajo el TTS y pasando el GF99 debajo de la Deco):
Edit: Y acabo de escribir Andy Davis para un par de dudas:
Actualización a 09/07/2023: Estoy ENCANTADO.
P.D: La App del móvil:
Actualización a 22/07/2023: Hoy se me ha olvidado en casa! :(
As it happened, the 20/80 GF soon became a popular “norm,” typically giving a deep stop similar to Pyle’s and the bubble models. ... Many are themselves using Bühlmann, but with the low GF value of 40 or 50 instead of 20. ... For Bühlmann ZHL-16C, GF low settings lower than 55 led to first stops that were considered to be too deep. The study mentioned that a GF Low of 70 was also acceptable, so it explicitly approved of a range of 55-70 but did not specify an upper limit. It also said a GF high of 70 or below was within the preferred US Navy limits.
Actualización a 26/08/2023: Primera carga desde que lo compré y cargué por primera vez (llevamos 7 inmersiones):
En su cuna (conectada al ordenador por USB) y sin quitar la correa NATO.
Actualización a 22/09/2023: A ver...
Actualización a 02/10/2023: Pensando en cambiar los GF ya que ayer me comí una buena deco cuando los demás ni entraron con los Suuntos:
Bien, según tengo leído:
As it happened, the 20/80 GF soon became a popular “norm,” typically giving a deep stop similar to Pyle’s and the bubble models. ... Many are themselves using Bühlmann, but with the low GF value of 40 or 50 instead of 20. ... For Bühlmann ZHL-16C, GF low settings lower than 55 led to first stops that were considered to be too deep. The study mentioned that a GF Low of 70 was also acceptable, so it explicitly approved of a range of 55-70 but did not specify an upper limit. It also said a GF high of 70 or below was within the preferred US Navy limits.
Y:
I choose my GF low to be about 83% of the GF high, for instance GF 70/85. Although the algebra is not exact, this roughly counteracts the slope of the “b” values. This approach allows me to believe I have chosen my GF rationally, is not so large a GF low as I am unable to convince my buddies to use it, and satisfies my preference to follow a relatively shallow stops schedule.
Bien, si quisiera seguir saliendo a GF High 70 (por defecto en modo técnio), tendría que usar un GF Low de 58,1 (83% de 70) en vez del GF Low 30 por defecto.
Actualización a 03/10/2023: Pues, me cuadra con el 40/85 del Rec:
Voy a empezar a probar, poco a poco, con el GF Low ya que mantengo el High conservador (70 del Tec u 85 del Rec). Es decir:
Actualización a 01/07/2024: Finalmente se hizo la charla y mandé un correo a uno de los ponentes. No me ha respondido a varias dudas sobre personalización del algoritmo.
Ayer mismo actualicé yo tanto App (a v2.11.7) como firmware del Teric (a v30) y me dió bastantes problemas (la App se quedaba colgada).
Actualización a 04/10/2024: Cierto, tengo que personalizar la pantalla del modo recreativo ya que no me muestra algún dato que considero necesario. Por ahora, voy a sacar fotos de los dos modos para comparar.
Actualización a 14/10/2024: Ayer buceamos en Tech y esta es la pantalla:
Me falta sacar una foto del OC Rec y personalizar.
Actualización a 05/11/2024: Ok, pantalla del Rec:
Y la acabo de cambiar para que me muestre el GF99 y T1, como en el Tech, que es lo que echaba en falta:
OC Tec: De 30/70 a 58/70. OC Rec: De 40/85 a 70/85.
Los GF(Lo)s del libro son bajos (5-35?) y los GF (Hi)s altos (70-150?). Aunque también es verdad que habla de hacer paradas más profundas y anticipadas para poder terminar las inmersiones de forma más agresiva.
Actualización a 06/01/2025: Vuelvo a cargar (taba a 0%) y actualizo firmware a la V33 y Cloud a 2.12.2:
Actualización a 23/05/2025: Perdix 2:
Actualización a 27/06/2025: Lo he puesto a cargar (15:54) hace un rato (estaba a 0%):
Nota: Miedo tenía con todo el lío que tenemos últimamente pero...
Shearwater Cloud Release Notes v2.12.5 Date: 2025-06-17 Fixes: -Fixed Bluetooth error 355 with older Firmware -Resolved firmware version in the Dive Log Computer panel -Prevented repeat syncing when UDDF logs contain no samples -Fixed Download Dives panel including hidden logs in count. -Temperatures outside sensor range are no longer shown -Fixed a bug where Tern TX models were being identified in some logs as Tern. -Standardized “TX” casing (formerly “Tx”) -Mobile: Fixed Bluetooth-permission warning mistakenly showing in Bluetooth Legacy mode. -Mobile: Can now download diagnostic logs -Mobile: Fixed max-depth sorting for locales that use commas as decimal separators -Mobile: Fixed consecutive auto-connect attempts -Android: Bluetooth/Location permission prompt can no longer be dismissed -Desktop: Fixed an issue where the dive list wouldn't return to scroll position after syncing.
P.D. Mañana haremos primera del año con trajes abiertos:
-Ajuste de presión parcial de oxígeno para acelerar la deco:
-Después del tratamiento: 3 semanas sin bucear y no volver al buceo profundo.
-Conclusiones:
PIENSA que aleteo mucho en el fondo por no encontrar el pecio y no usar
scooter y fue un error no avisar del frío en una de las piernas (aunque
sí lo hizo con el dolor abdominal que asoció a lo que comió y resultó
ser un Spinal bend DCS) durante el ascenso y le queda la duda de si una
parada profunda habría solucionado el problema.
-Discusión sobre los GFs en los comentarios:
-Sobre el dolor abdominal:
Actualización a 25/09/2025: A ver si le puedo sacar más jugo a ésto:
The @+5 option is particularly useful. It shows what the TTS will be in 5 minutes, assuming the diver stays at the same depth.
This can be used for looking ahead. If you know your maximum TTS, then
you can compare this against your current TTS to see if you have reached
your limit, but the @+5 setting allows you to look ahead 5 minutes and
see what your TTS will be in the future. You can use this to decide
whether you have time to look at another piece of the wreck or whether
you must turn around and head back to the shot-line. This is
particularly important at deeper depths where the rate at which
decompression is built up is much faster, and a large amount of deco can
be incurred in a relatively short period of time.
The Δ +5 option shows the difference (the delta or Δ) between your TTS right now and what your TTS will be in 5 minutes.
For example, if your TTS is 20 mins and your @+5 is 30 minutes then the
Δ +5 would be 10 minutes (30 – 20 = 10). In other words, in 5 minutes
time, you will have incurred an additional 10 minutes of deco more than
you have right now. This could be done manually, but in some situations,
it is nice to be able to see the delta without having to constantly
make that calculation. The size and magnitude of this figure can also be
used to tell the current state of your decompression. If the Δ +5 is
positive, this means that you are on-gassing and will have more
decompression in 5 minutes than you have right now. If Δ +5 is 0, then
you are neither ongassing or offgassing and you will have the same
amount of decompression in 5 minutes as you have right now. Finally, if
the number is negative then you are offgassing and you will have less
decompression in 5 minutes than you have right now. This is
particularly useful for multi-level dives. Let’s assume you are on a
deep reef and you notice that your TTS is approaching your maximum TTS.
You ascend a few metres and you notice that your Δ +5 is now +1. This
means that you are still incurring additional decompression, although at
a much slower rate, and so your TTS will continue to increase. If you
come up a few metres more, you can now see that your Δ +5 is zero. This
means that you are neither ongassing or offgassing and you can stay at
this depth without increasing your TTS. If you ascend slightly shallower
and your Δ +5 changes to -1 then you can see that you are now
offgassing and you can stay at this depth almost indefinitely as your
TTS will slowly reduce.
The settings above can be used to
proactively manage the dive and can be used on any dive. There are
several other options that would primarily be used in an emergency to
change some of the dive parameters on the fly.
The CEIL option
shows the raw decompression ceiling. Once the diver goes into
decompression, they can no longer ascend directly to the surface, and
there is a depth at which the supersaturation would exceed the maximum
allowed. The decompression ceiling is the exact depth at which this
would occur. This is slightly different from the decompression stops
shown on the computer as the deco stops are rounded to the nearest 3m
increment below the actual decompression ceiling. The actual value of
the ceiling will slowly get shallower during the decompression, but the
decompression stops will stay at the 3m increment until the ceiling
reaches the next 3m increment. At this point, the decompressions stop
will jump up to the next 3m increment. By comparing the decompression
stop and the CEIL value you can see how much margin for error you have
at that stop or how close you are to the end of the decompression stop.
If your computer shows a 9m stop and your CEIL is 8.9m then you can see
that the ceiling is only slightly above the current decompression stop
and so there is very little margin for error in your position in the
water column, and you also know that you will be at 9m for some time to
come. As the CEIL moves up and gets to 8m then 7m and then 6.5m you know
that your decompression stop is coming to an end. This can be useful to
know if, for example, you are decompressing on a line at 9m along with a
number of other divers. If it is getting crowded on the line at the 9m
stop, but you know your CEIL is showing 6.5m then you can move up to 8m
or 7m without breaking your ceiling. Your computer will alert you that
you are above your decompression stop, and if you stay at that depth, it
will give you a MISSED DECO alarm but you know that despite this you
are in fact below your decompression ceiling.
The next setting
that it is possible to select in the NDL space is the GF99 setting. This
is useful information to know as it shows the current GF, in other
words, how close you are to the M-Value which corresponds to a gradient
factor of 99. Whether a diver selects his own gradient factor settings
or makes the decision to use the default settings, the computer will
display the ceiling, decompression stops, as well as the time to
surface, based on these gradient factors. If the diver is using 30/80
gradient factors, then during the ascent up to the first stop the GF99
should be approaching 30, as the first stop is calculated as being at
the point where the GF is at 30% of the M-Value. At the surface, the
GF99 will be 80, as the high GF determines how close the diver is to the
M-Value on surfacing so a GF Hi of 80 means the diver should be at 80%
of the M-Value as they surface. For intermediate decompression stops,
the GF99 will slowly increase from 30 on arrival at each subsequent
stop. During each deco stop, the GF99 should slowly decrease as the
tissues offgass and the ceiling increases. Once the stop clears and the
diver moves up to the next stop, the GF99 will again increase. This
allows the diver to “see” the offgassing taking place as it shows that
as they offgass, the level of supersaturation is dropping, and they are
moving further away from the M-Value.
If the GF99 is much
lower than 30 on the initial part of the ascent or does not slowly
increase on the ascent up to each subsequent stop, then the diver is
ascending slower than intended. The TTS shown assumes the diver will
be ascending at the prescribed ascent rate. If the diver is ascending
slower than the correct ascent rate or stops below the decompression
stops, then they are, in effect, lagging behind the calculated
decompression schedule. The result of this is that the diver is not
offgassing as quickly as the model has assumed, and so the diver will
take longer to decompress. In extreme cases, the diver may still be
ongassing in some tissues, and the slow ascent may actually increase the
decompression requirement. As a result, the actual ascent time may be
considerably longer than the calculated TTS. If the diver is using the
calculated TTS to manage their dive as described above, this can cause a
problem as the gas planning assumed that they would be following the
calculated decompression schedule. By causing additional decompression
time, they will end up requiring additional gas for this extra time.
If
the diver ascends above the deco stop, the computer will give a
warning. As we have already seen, you can ascend above this deco stop,
but still, stay below your decompression ceiling as shown with the CEIL
display. If you ascend even further beyond the CEIL depth, the GF99 can be used to provide some additional information.
For example, if the diver has set a GF Lo of 30% and ascends above
their initial deco ceiling, the computer will give a warning. The GF99
may still show that they are only at 40% GF which, although it is beyond
both their deco stop and deco ceiling, is still well within the
M-Value. Similarly, for the later stops, if the diver has set a
conservative GF Hi of 70% and ascends above their deco stop, the
computer will give a warning. The GF99 may still show that they are at
80% GF which is still well within the M-Value. However, if the GF99
shows more than 100%, the diver is now well over their M-value and is in
a much riskier position.
The same goal can partly be achieved in
the Dive Settings menu where it is possible to change the high gradient
factor during the dive. By changing the high gradient factor from, say
70 to 80, you would reduce the rest of the remaining decompression.
Although it is possible to change the high gradient factor in this way,
it is not possible to change the low gradient factor, and so the initial
stops would be unchanged.
This functionality is not intended to
be used on a regular basis, and the diver should stay within the
ceilings indicated. However, in an emergency, this functionality may be
very helpful. For example, assume that a diver on a decompression dive
is running low on gas. Their computer tells them that they have another 5
minutes of decompression to do before they can move up to the next
decompression stop where there is more gas available. They could edge up
from the current stop to the next stop while watching their GF99
setting. Even though they are breaking their decompression ceiling they
can use the GF99 display to show them how close they are getting to
their M-Value, and can then make an educated decision on what is the
more important risk.
These last few options may seem worrying, or
even dangerous, but remember that the stops are determined by the
gradient factor settings. If you are using a GF of 70 then you may have a
deco stop which would not be present if you had selected a GF of 80.
So, missing a deco stop using a 70 GF, but still staying less than 80 on
the GF99 display is equivalent to staying within the deco stops on a GF
setting of 80%. In fact, you may have deco stops, while the underlying
Buhlmann model, which is based on a maximum gradient factor of 99, may
indicate that it is within the No Decompression Limit. This is
completely normal for the first few minutes of going into deco. If you
have your GF settings set to anything less than the maximum value of
99%, then a GF profile will always go into deco before the underlying
Buhlmann NDL limit is reached.
The same approach could be adopted with ascending
all the way to the surface. In a critical emergency, the diver could
edge up towards the surface watching their GF99 display and making sure
that they stay close to, but not exceeding, their M-Value. However, this
case can be managed more effectively using the Surfacing GF display
feature. This is a newer feature, and may not be available on your computer unless you have updated the software recently. The
Surfacing GF displays the GF that you would get if you were to ascend
directly to the surface right now, without doing any stops.
If
the SurfGF display shows 50, this means that if you were to ascend to
the surface directly, your maximum tissue saturation would be 50% of the
M-Value. I.e. well within your M-Value limit with almost no chance of
DCS. If your SurfGF shows 150%, this means that a direct ascent to the
surface would put you at 150% of your limit, and well over the M-Value
limit with a very high chance of DCS. Finally, if your SurfGF shows 99,
then a direct ascent to the surface would put you right on your M-Value
limit and is equivalent to the NDL limit of a straight Buhlmann model.
Interestingly, you can be in deco but still have a SurfGF of less than
99. Remember that the deco stops are based on your selected GFs. If you
have the default GF setting of 30/70, then you will start to get deco
stops well before you reach the underlying NDL limit. So, if you have 5
minutes of deco shown on your computer but your SurfGF is 90 this means
that you have 5 minutes of “GF Deco”, but you have not yet reached the
NDL of the underlying Buhlmann model. This means that, in an emergency,
you could still go straight to the surface without breaking the Buhlmann
decompression schedule. This is very different from the situation where
you have 15 minutes of deco and your SurfGF display shows 120. In this
case, you have “GF Deco” as well as “Buhlmann Deco”. If you were to go
straight to the surface, you would not only miss the deco stops
indicated on the computer, but would also end up being over your M-Value
on the surface and have a significant risk of DCI.
The SurfGF feature can be used at any point of the dive, not just at the start of the ascent. For example, you
can track your SurfGF during your ascent and deco. Once your SurfGF
drops below 99, you know that from that point onwards if there is an
emergency, you could go to the surface and still be within the Buhlmann
limits. Equally, you can use it the other way around. After your deco
stops have cleared, you can monitor the SurfGF to see your updated
SurfGF. One technique that can be used is to have a slightly more
aggressive high GF such as 80 or 90 to reduce the mandatory
decompression stops but then wait until the SurfGF has dropped to a
lower level as a “safety stop”.
As the tools available to
divers continue to change and improve, it is inevitable that the
techniques used must also change to make the most of the available
tools. This article is intended to show that, far from removing the need
to plan a dive, the sophisticated dive computers available today can
help to improve the planning process. They can be used to provide a more
realistic and more flexible planning tool. They can also be used to
adapt the plan when the situation changes. This is only possible if the
diver understands the tools they have at their disposal and practices
using them. After reading and digesting the information contained in
this article, I would encourage you to make sure you know where to find
the various display options on your computer. On your next dive look
at the SurfGF value during the dive and watch the relationship between
it and the NDL value. During the NDL ascent, look at the GF99 and SurfGF
values. Then on a decompression dive, compare the CEIL and Stop Depth
values as well as comparing the CEIL, GF99, and SurfGF values. It is
essential that you understand all of the information in this article
and practice it before using it to plan your dive or modify your dive
plan. Like any tool, you must practice before using them for real.
However, a bit of investment in time and practice will give you the
ability to manage your ascent in a much more intelligent way than
blindly following your computer or a fixed set of deco tables.
When the dive log is transferred to Dive Shearwater, the log will display: -Your dive location on a map -A location name (if available) -Entry and exit coordinates -A world view of all your dive log locations -If a user has multiple transmitters, only 1 needs to be GPS.
LOCK IN YOUR LOCATION: The Swift GPS uses a multi-constellation Global Navigation Satellite System (GNSS) receiver that determines location from GPS, Galileo and BeiDou satellites. The location information can can be shared with your buddy or a boat full of divers. Any Shearwater air-integrated computer within range can pick up the Swift GPS signal.* *GPS function does not work underwater
Actualización a 19/11/2025: Ah, vale. Que la App tampoco está disponible todavía:
De: Service Center Operations Coordinator (Shearwater Research) <info@shearwater.com> Enviado: martes, 18 de noviembre de 2025 19:11 Para: Storm Asunto: Shearwater Research Re: Dive Shearwater App in Google Play Store
##- Please type your reply above this line -## Your request (191549) has been updated. To add additional comments, reply to this email. Service Center Operations Coordinator (Shearwater Research) Nov 18, 2025, 10:11 PST Hello Storm,
Thanks for reaching out to us.
The app isn't available yet. It should be available for download on December 1st.
Best,
--
Ivan Ljubka Shearwater Research Inc. www.shearwater.com 100 - 10200 Shellbridge Way, Richmond, BC V6X 2W7 P: 604-669-9958
Ya decía yo.
Actualización a 01/12/2025: Tengo que mirar bien esto sobre el GF99:
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