Computer that Displays SAC During Dive

[Triker]

I like to try different equipment in different scenarios and want to know how changing each variable affects my SAC. It is, for me, a good indicator of my mental state. I currently have an Oceanic Veo 2.0 and would love to get an air-integrated computer that displays SAC during the dive. I know I can calculate SAC after the dive, but that is an average of the whole period, not a short window. I was holding out for the Atomic Cobalt 2 however am not sure it will display SAC during the dive. I do not believe the old one did however I have seen indications the UI will be changing.

TLDR: Are there any computers out there that display SAC during the dive?

Thanks,
Todd

 

[Akimbo]

The problem with continuous display of SAC rate is the sensors aren't accurate enough to display it breath by breath. Therefore it must average over some period of time. The problem there is the longer the period of time the less useful it is as a means of monitoring your usage — but the calculation becomes more accurate.

Perhaps a more effective indicator would be the heart rate monitor available on the Scubapro Galileos? However, I would suggest that you get more dives in before making that investment. There is a lot of value in learning to monitor your physical state without depending on a single indicator.

 

[Mr Carcharodon]

Well you could use the tank factor approach.

To do this calculate the number of cubic feet of gas per 100 psi. So for example if you dive a high pressure 100: 100 cubic feet/35=2.86. But 2.86 is impossibly precise to use. In practice you will round to an easy number like 3.0 or 2.5. In this case 3.0 would be used. 3.0 would be your tank factor. This means you use 3.0 cubic feet of gas per 100 psi of gauge pressure. Now let’s say your SAC is 1.0 cubic feet per minute at 1 ATA. At 66 fsw you would be at 3 ATA so your DAC would be 3.0 cu ft per minute. Based on your tank factor your expectation is for each minute of dive time your pressure gauge should go down by 100 psi. Working this out for other depths may require some approximation but with practice this is not difficult. That is the approach of using the computer between your ears.

 

[RonR]

To calculate SAC inside a dive computer there needs to be a way to input the tank size, and most computers don't have this. The Cobalt has this ability, and displays SAC in the dive log as an average for the whole dive. It doesn't show it during the dive- we try to show only essential information. In any case, Akimbo is correct in that the sensors, being accurate to only around 10-15 psi reliably, aren't going to have the resolution to deliver this data minute my minute.

Ron

 

[tomfcrist]

To calculate SAC inside a dive computer there needs to be a way to input the tanks size, and most computers don't have this. The Cobalt has this ability, and displays SAC in the dive log as an average for the whole dive. IT doesn't show it during the dive- we try to show only essential information. In any case, Akimbo is essentially correct in that the sensors, being accurate to only around 10-15 psi reliably, aren't going to have the resolution to deliver this data minute my minute.

Ron

I think you mean RMV. SAC measures PSI used, RMV involves actual volume of air in which case your post would be correct.

 

[Insta-Gator]

I think you mean RMV. SAC measures PSI used, RMV involves actual volume of air in which case your post would be correct.

There are a number of threads arguing the terminology. . Let's stick with the op intended meaning.

IMO monitoring sac/rmv continuously would be meaningless and the added taskloading would make it worse.

Sent from my SCH-I535 using Tapatalk

 

[Akimbo]

I think you mean RMV. SAC measures PSI used, RMV involves actual volume of air in which case your post would be correct.

Good point. The Cobalt actually labels it as “Gas Consumption Rate” expressed in Liters or Ft³/minute. In fact, RMS is a much more useful value for the OP’s purpose.

Ref:
What Is a Surface Air Consumption Rate (SAC Rate)?
What Is a Surface Air Consumption Rate for Scuba Diving - SAC Rate Definition - SAC Rates vs RMV Rates

What Is a Respiratory Minute Volume Rate (RMV Rate)?
What Is a Respiratory Minute Volume Rate in Scuba Diving - RMV Rate Definition - RMV Rates vs SAC Rates

 

[RonR]

I think you mean RMV. SAC measures PSI used, RMV involves actual volume of air in which case your post would be correct.

You're right, I was misreading the OP's intent. The Cobalt actually displays RMV, the surface- equivalent consumption in either Liters³ or Ft³ per minute. For just surface-equivalent pressure drop comparisons you wouldn't need to know the tank size, just pressure and depth. Questions about the resolution of the sensor would still apply, though.
I'm fairly sure there have been some dive computers that displayed a kind of "fuel efficiency" type graph that was supposed to give you your breathing rate during a dive, but I can't recall who from at the moment.

Ron.

 

[pjhansman]

Good point. The Cobalt actually labels it as “Gas Consumption Rate” expressed in Liters³ or Ft³/minute. In fact, RMS is much more useful value for the OP’s purpose.

Oceanic's Oceanlog software calculates and displays SAC as a volume (cu ft.) per minute. Call it what you will...that's the number I'm most interested in.

 

[RonR]

Some of us old folks used to talk about "surface-equivalent air consumption" expressed in CF- for which you need to know the tank size. That's what my aging synapses picked up from the OP. But I believe RMV (respiratory-minute-volume) has long been the accepted technical expression for this.
Most dive log software will calculate this, but few dive computers will do it onboard since most know only the pressure drop and depth, not the tank size.

Ron