Minimum gas answers how much must I keep to get two of us up? It works out rock bottom: the gas a team needs to sort out a problem at depth and ascend together, breathing hard, from one cylinder. Reach that pressure and the ascent starts.

What you enter

• From (m): the depth the problem happens at, usually the deepest point.
• To (m): 0 m for a direct ascent, or your first gas-switch depth.
• Rate (m/min): the ascent rate.
• Divers: how many breathe from this gas. Two is you and a buddy out of gas.
• Stress factor (×): how much faster than your RMV everyone breathes during the problem.
• Sort it out (min): time at depth before the ascent starts.
• Stop (min): time at the stop on the way.
• RMV, Water and your cylinder: shared with the other consumption tools. Start sets the rail, not the result.

The Problem group notes that two divers at a stress factor of 2 is the usual rock-bottom assumption.

Reading the result

• Keep at least (bar): the main figure. Its rail runs to your full Start pressure, marked solid, and turns red when rock bottom is more than a full cylinder.
• Gas for the ascent (L): the same reserve as free gas.
• Ascent (min): the time from From to To at your rate.
• Average ambient (bar): the pressure the ascent is breathed at, on average.

The figure adds three parts, each breathed by every diver at RMV times the stress factor: the time to sort it out at the From depth, the ascent at its average depth, and the stop at the To depth. A stop is never counted shallower than 3 m, so a direct ascent still pays for its stop. Figures round up: litres to the whole litre, pressure to the next 5 bar.

The verdict gives the instruction, for example Start the ascent by 115 bar, so you and a buddy out of gas can reach the surface.

What it does not include

• Anything after the To depth. Decompression below it, further stops and later gases are not counted.
• The rest of the dive. Rock bottom is a floor to keep, not the gas you need to dive.

Next

• Turn pressure plans the outbound leg around a reserve; compare its Reserve with this figure.
• Contingency re-plans a whole dive that runs long or deep.