Ayisha
Contributor
...the goal should be to be able to estimate what the minimum reserve is at your current depth, no?...
No.
Rock Bottom gets re-calculated when you safely ascend to a shallower depth. New depth, new rock bottom.
1 Minimum Gas gets calculated for a max depth if you are doing a MD ascent. That's it.
Lamont had an excellent essay on calculating the early RB on SB many years ago. He then removed it and replaced it with the next version of rock bottom, which was more conservative. That essay is probably still on here. I had a copy of both on a very old hard drive and backup (2004 or 2005?). It would be a PITA to search for them.
However, this is a very old mac-tacked table (both sides) I made from the original RB way back when, with some moisture damage:
I never made a table of the next version of Rock Bottom as it was pretty much a non-starter for a single tank, and that is when the advice came out to limit a dive depth to the cf of a tank, for example, an 80 cf tank to a max depth of 80 feet.
Not sure how it evolved after that when other DIR groups ran with it.