Here is the scenario. My wife/dive buddy has been diving a jacket style bcd which weighs 8.7# dry, and with her total gear configuration (including that bc) needs 14# of lead in SW. We know that weight is correct because with any less weight she starts to float with an empty bc and with 700 psi at the safety stop. She recently bought a jacket style travel bc that weighs 5.5# and all other dive gear remains the same. Although the weight of the two bcds only varies by @3#, the lighter bc may not have the same inherent buoyancy as her 8.7# model. Although she will do a proper weight check on our next dive, which unfortunately will be on a cruise, and we hate making other divers wait while we fiddle around with weights at the start of the dive. So to put her in a reasonable ball park for start the dive weight, is is valid to do a buoyancy test on the two bcs to see how much difference in lead is required to sink both bcds, and use that difference to add or reduce the start dive weight for her new travel bcd? I suspect that the travel bc will require less lead, but I am not discounting the difference in actual bcd weight because I do not know the inherent buoyancy of either bc. Thanks for the advice.