Calculating your Breathing Rate or Respiratory Minute Volume (RMV).Well, now you know some of the theory of planning for air capacity requirements. When you put it in practice, go over your planning with a more experienced diver. You can also make your calculations more accurate by knowing your own personal surface breathing rates under various workloads and conditions. One way to work out your breathing rate or RMV (Respiratory Minute Volume) is by observation.
During a dive, monitor and record your pressure gauge and time spent at a particular depth. To work out your RMV, time how long it takes to consume a given amount of air at a particular depth.Make a number of observations and note your exertion level to get an even better idea of your consumption under a variety of conditions.
Example: You reach 10 metres depth and your gauge pressure is the equivalent of 200 atmospheres (about 203 bar or 2940 psi; 1 atm = 1.013 bar or 14.7 psi). After 30 minutes at this depth you observe your gauge is now
80 atm (about 81 bar or 1176 psi). You know your tank has a WC (water capacity) of 10 kg.
(RMV = 1200 / (30 x 2))