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# Two computers, or tables?
- URL: https://www.techdiving.com.au/two-computers-or-tables/
- Published: 2026-09-30T05:41:14.000Z
- Updated: 2026-09-30T05:41:14.000Z
- Description: Dive computers now run full trimix decompression. Should you trust two of them, or plan the dive on paper and dive the plan? Most divers do some of both.
- Author: Tech Diving AU
- Tags: Gear, Deep/Trimix, #Import 2026-09-30 15:24

Twenty years ago, many technical divers planned every dive on a laptop, printed runtime tables, and dived with a depth gauge and timer. Today, trimix computers are common and reliable. But the old approach has a strong case too, and many experienced divers still use it.

Instruments

### What should you rely on underwater?

Two ways to manage decompression during the dive.

#### Dual computers

Two trimix computers, often from different makers, set to the same plan and gases.

Why divers choose itAdapts to the dive you actually did, including extra time or depth. Redundancy if one fails. Less arithmetic underwater.

Watch out forIt's easy to stop thinking about decompression. Different algorithms or settings may disagree at the worst moment.

#### Tables and bottom timer

A pre-planned runtime with contingency tables, followed with a bottom timer or gauge-mode computer.

Why divers choose itThe whole team shares one plan and knows it before the dive. Forces you to understand your decompression.

Watch out forRigid when the dive changes. Planning errors travel with you, and following tables under stress takes discipline.

**Common ground**Most divers now carry a computer and a written plan. Know what you'll do if both fail.

## The case for two computers

A computer tracks the dive you actually did. If you go deeper or stay longer than planned, it adjusts. That makes it more forgiving of the small changes that happen on almost every dive. Carrying two gives you a backup if one fails.

Using computers from two different makers, both running the same algorithm and settings, protects against a software fault that could affect both units at once.

### Watch the settings

Two computers only help if they're set up correctly. Check that both have the same gases, gradient factors or conservatism level, and that you know what each one will do if you switch to a gas it doesn't expect.

## The case for tables

A written plan forces you to think through the dive before you get wet: bottom time, gas switches, stop depths and contingencies. The whole team works from the same plan, so there's no confusion about when to leave a stop.

Contingency tables cover common changes, such as going a few metres deeper or staying five minutes longer, or losing a deco gas.

## Combining both

Many divers use both. They plan the dive on software, carry a written plan with contingencies on a wetnotes page or slate, and dive with one or two computers. If the computers agree with the plan, good. If they don't, the difference is a signal to stop and think.

## A simple set-up checklist

- Both computers use the same algorithm and settings.
- All gases are entered correctly and match your analysed cylinders.
- Your written plan includes lost-gas and deeper-longer contingencies.
- Your team knows whose computer or plan leads if they disagree.
- Batteries are charged and firmware is up to date.