Organize completed dive logs, match cylinder and segment records, distinguish SAC and RMV units, reconcile gas use and retain sources for later review.
Choose a completed dive and keep its date, site, buddy or instructor, equipment configuration and original computer or written log together. Preserve the exported profile where available. Note the source and units of depth, duration, pressure and temperature readings. Keep reported observations separate from values reconstructed later; a missing reading stays missing rather than becoming zero.
Identify the start and end readings for the same cylinder and completed segment. Record how elapsed time was defined and whether the window included surface activity, inflation, sharing gas or a suspected leak. Keep the actual cylinder rating with the readings. Do not combine one cylinder’s capacity with another’s pressure rating, or merge several cylinders into one pressure drop.
Use the pressure-window tool only when the required rating pair, pressure endpoints and an independent gas-use record are available. The rating must pair surface free-gas capacity with its matching rated gauge pressure; internal water volume alone is not that capacity. Compare the reproduced result with the independent record and investigate differences in source, units or rounding. Retain the result as an approximation for this completed window.
For SAC/RMV, add the elapsed segment time, documented average absolute ambient pressure in ATA and an independent RMV record. Use an average that belongs to that same segment; maximum depth is not an average-pressure record. Keep pressure SAC, pressure-normalized RMV and surface-equivalent gas used per elapsed minute as separate quantities. If a required source is unavailable, retain the raw log and the unresolved question instead of inventing inputs.
Record workload, conditions, equipment changes and anything unusual while the details are fresh. Compare calculations only after confirming compatible definitions and units. Cylinder gas loss can include inflation or leaks as well as breathing; the result is not a lung-function test or a fitness score. Discuss unexplained discrepancies or equipment concerns with an appropriate instructor or service professional, keeping the original readings intact.
Save each completed calculation using its manual save button, and keep the source log and equipment identifiers with your records. Download this guide’s plan after marking completed preparation and review tasks. Maintain a backup of original dive files outside browser storage, and record who will resolve outstanding questions. A historical gas-use value alone does not establish future reserves, turn pressure, dive duration or decompression requirements.
Reproduce surface-equivalent gas used for one completed cylinder pressure window from a matched rated free-gas capacity/pressure pair and compare an independent gas-use record. This does not estimate remaining dive time.
Reproduce pressure SAC and RMV for a named completed segment using its documented average ATA, elapsed time and cylinder rating. Distinguish pressure-normalized RMV from unnormalized surface-equivalent gas use per elapsed minute.
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Names and units must travel with the value. These worksheets reproduce completed records using a linear cylinder-rating approximation.
| Quantity | Meaning | Do not confuse it with |
|---|---|---|
| Pressure SAC | Pressure drop per minute divided by average ATA; psi/min or bar/min | A volume rate that can be transferred between cylinders |
| RMV | Pressure SAC multiplied by the documented cylinder volume/pressure ratio | Unnormalized cylinder gas use per elapsed minute |
| Surface-equivalent gas use per elapsed minute | Surface-equivalent volume used divided by elapsed minutes | Physical gas volume flow at ambient pressure |
Educational arithmetic only, not a dive plan. A matched rating is 2400 surface liters at 200 bar; readings fall from 200 to 140 bar over 20 minutes with a documented average 2 ATA. The independent RMV record is 17.5 L/min.
| Calculation | Result |
|---|---|
| Cylinder constant: 2400 / 200 | 12 surface L/bar |
| Surface-equivalent gas used:(200 −140) ×12 | 720 surface L |
| Gas use per elapsed minute: 720 / 20 | 36 surface L/min |
| Pressure SAC: 60 / 20 / 2 | 1.5 bar/min |
| Normalized RMV:1.5 ×12 | 18 L/min |
| Reproduced minus independent RMV:18 −17.5 | +0.5 L/min |
Use these sources to understand recordkeeping and the distinct gas quantities. The examples here are retrospective arithmetic; reserve, ascent, decompression and other future-dive decisions require the appropriate training and planning process.
Add an explanation when correcting a transcription; retain the original source so the change can be checked.
Matching units are insufficient if one record covers an entire dive and another covers only a segment.