While diving the Vandenberg, we were setup for two 100-feet+ dives running 30.2 and 30.8 percent nitrox mixes. For those that are not familiar with nitrox gas or diving, it is a mixture that contains more oxygen but has inherent hazards in that going below the prescribed depth can lead to oxygen toxicity and death. Divers train to know what these depths are and set their computers or their dive profiles accordingly. At the time we measured, we decided we would simply round up the values thinking that max depth would be calculated as a higher value and thus our computers would be more conservative. The divemaster suggested we actually round down instead, to ensure that we have the proper dive time profile for nitrogen in the computer, especially when setting the computer to a 1.4 conservative profile for max depth anyway. An interesting debate!
Ultimately, both are true and to be a purist one should probably round up to calculate your max depth and set your computer to the rounded down value to be more conservative on nitrogen. That said, the nitrox sensors themselves are rarely accurate to even a percentage so many online discussions on this topic suggest the best de facto way would be to simply round to the nearest value: i.e. 30.2 as 30 and 30.8 as 31. So from now on, this is what we will do.