Depth Averaging
The easiest way is to break bottom part of the dive into 5 min segments. Average each 5 min segment. Take the deepest segment and the shallowest segment and add them together. Divide by 2. This will give an average for the dive. Now weight it for depth and time. Meaning if you spent more time deeper then weight towards that depth. If you
spent more time shallower, then weight towards shallower.
Example: Dive on 21/35 using nitrox 50 for deco and the dive profile is 100’/30m for 5min then 150’/45m for 5 min then 160’/48m for 5 min then 140’/42m for 5min then 130’/39m for 5 min then 100’/30m for 5 min. Total 30 minutes you would do this:
So deepest is 160’/48m + shallowest 100’/30m = total of 260’/78m divide this by 2 to equal 130’/39m. About half the dive was spent shallower than this, and the other half at this depth or deeper, so we can use this average without adjusting to weight for depth. Using the average of 130’/39m, the deco would be 20min on nitrox 50 for a 30min bottom time.
A conservative approach to weighting is to average each of the bottom time segments pair wise, starting with the shallowest. In detail, find an average depth for each 5 min segment. Then, sum the depths of first two shallowest segments and divide by 2. Then use that average and sum it with the depth of next deepest segment and divide by two.