Hilton Tnunay

CMAS/POSSI DIVE CHART

Dive planning tables

Plan each dive. See how the surface interval changes your next bottom-time allowance.

Diving Automated Calculator
Check against the official CMAS/POSSI chart before use. This chart is only to automate the planning according to official chart, not a certified dive planner.

Section 1 · Repetitive no-decompression planning

For non-military diver, use the red limits

Dive profile

Square-profile diagram · depth is proportional; horizontal spacing is schematic. Scroll sideways for longer sequences. Group boxes mark the start and end of each dive.

Your dive sequence

Example inputs are loaded. Replace them with your plan. ABT follows your training’s bottom-time convention.

Table calculations

Updates as you type
How the calculations work

TBT = RNT + ABT · Maximum ABT = TBT max − RNT.
TBT max (NDL) is the selected no-decompression time limit at the table depth; it includes RNT. A negative allowance means there is no available no-decompression time; the displayed maximum ABT is capped at zero.

  1. Convert metres to feet (1 ft = 0.3048 m), then round depth up to the next printed row. First dives below 25 ft use 25 ft; repetitive dives below 40 ft use 40 ft because the residual table starts there.
  2. Round ABT up to a whole minute, then use the next group-time cell at or above TBT. Blank cells are skipped.
  3. For the next dive, round the surface interval down to a whole minute and look up the reduced group, then RNT at the next dive’s table depth.
  4. Surface intervals below 10 minutes are unsupported. Only an interval strictly longer than 12 hours clears the previous group under this chart; exactly 12 hours remains repetitive.
  5. If TBT exceeds TBT max, later dives are blocked. Decompression schedules, emergency procedures, ascent limits, altitude, nitrox, flying and gas reserves are outside this calculator.

“Within selected limit” describes the table calculation, not a guarantee against decompression sickness. Follow your instructor’s current procedures and track actual exposure using the same planning method.

View the official CMAS/POSSI non-decompression dive chart

Source: CMAS/POSSI dive chart.

Supplied CMAS/POSSI dive chart with depth and group tables, surface interval matrix and residual nitrogen times.
Terminology
RNT
Residual nitrogen time for the next depth.
ABT
Actual bottom time entered for this dive.
TBT
Total bottom time used for the table lookup.
TBT max (NDL)
Selected maximum table time without required decompression.
Group
The table letter used to carry residual nitrogen to the next dive.

Section 2 · Decompression dive planning

POSSI Table 4 · U.S. Navy air decompression table · Depths in feet.

Training table lookup — verify with your instructor. Values are transcribed from the supplied POSSI photograph. The two-row adjustment follows your requested training rule; that rule and its conditions are not printed in this photo and have not been independently verified. Complete operating instructions are still required for real diving. This isolated lookup assumes no residual nitrogen from previous dives.

Round depth up within 40–140 ft and time up to the next printed row, then advance two time rows in the same depth block. Outputs use the adjusted row. If the row is unavailable, the lookup stops. The first printed time row is accepted and receives the two-row adjustment. Inputs below that row belong in Section 1.

View the official CMAS/POSSI decompression dive chart

Source: CMAS/POSSI dive chart.

Open full-size POSSI chartPOSSI Table 4 air decompression chart and dive-profile worksheet.