Tips N Tricks : displaying your SAC Rate

SAC stands for Surface Air Consumption. So the simple definition of your SAC Rate is the rate at which you consume air when scuba diving. It is measured as some quantity over time, usually 1 minute and refers to how much you would consume on the *surface*, or at 1 atmosphere, over 1 minutes time.

Knowing your SAC rate gives you, the scuba diver, another piece of data about a particular dive and gives you an indication of how hard you worked, or how relaxed you were while diving. If you review your SAC rate over various dives and conditions, you'll get to know how long a particular tank will last you and this can assist in your future dive planning.

So what pieces of information are needed for Dive Log/Dive Log Manager/Dive Log DT to figure this out for you:
1. Average Depth over the length of the dive
- if you have a dive profile from a dive computer, your average depth will be calculated from the profile itself (this is the green horizontal line on the dive profile display). If there is no profile, you should enter your best guess at your average depth in the place provided.

2. Length of Dive
- again, this is obtained from the dive profile if there is one, but otherwise a time must be entered. Note that some dive computer manufacturers include the amount of time that you spent on the surface at the end of the dive in the total length of the dive, and some explicitly end your total dive time as soon as you reach a shallow depth. This extra time, or lack thereof, will effect the calculated SAC Rate.

3. How much air/gas you used, which needs:
a. Starting Tank Pressure and Ending Tank Pressure
- the difference gives the amount used in pressure units, like 2000 psi or 150 bar
b. The size of your tank
- if you're using metric units, the size of the tank is given in liters which makes calculations easier
- if you're using imperial units, the size of the tank is given in cu ft which doesn't tell you enough information. So you must also enter the working pressure of that tank. So if you have a high pressure 80 cu ft tank that is normally filled to 3500 psi, it will hold more gas than a low pressure 2200 psi 80 cu ft tank, even though they are both the "same size".
- and of course, if this "tank" is really a double, then there is twice as much available

So that's it. You'll see you're SAC rate listed next to the tank information on the Environment Tab in Dive Log Manager/Dive Log DT. Dive Log shows it as part of the Tank Details information.

And what about you techies who use more than one tank on a dive? Dive Log Manager/Dive Log DT will also give you a "per tank" SAC rate for the amount of time you used that tank, and then also give you the over all *dive* SAC rate for all tanks combined. Information for the calculation is taken from the dive profile information, and the tank switches, to determine the average depth for the time on a particular tank and then the SAC rate is calculated accordingly.

So, be sure to fill in all that information for each dive so you can also view your scuba dive SAC rate!