Intermediate 8 minutes
Instrumentation: pressure gauge, computer, and compass
What your instruments tell you, and what they can never know
A dive computer calculates your decompression using a mathematical model that has no idea whether you slept badly, whether you're dehydrated, or whether you're going to get cold during the safety stop. It's an excellent tool, and it has that limit: it's worth knowing both.
In this article you'll see what each instrument measures, how to configure a dive computer, what the conservatism setting means, and what role the compass and redundancy still play.
Instruments are your source of objective information underwater. Knowing exactly what they tell you, and what falls outside their reach, is part of diving with judgment.
The pressure gauge and gas management
The pressure gauge shows the pressure remaining in the tank and is the instrument you need to check most often throughout the dive. It can be analog, connected by a high-pressure hose, or wireless via a transmitter that sends the reading to the computer.
The analog gauge has the advantage of not depending on batteries or pairing, and of showing the reading continuously. The wireless version integrates consumption into the computer, which allows for air-time calculations and a more convenient reading, in exchange for depending on two batteries and a link that occasionally drops.
What matters isn't the type of instrument but the habit. Checking the pressure gauge regularly and on a plan, not just when you remember to, is the basis of gas management. Reserve criteria and consumption rules are covered in the planning category.
A practical detail: the needle on an analog pressure gauge doesn't drop linearly across its whole range, and many gauges have the reserve zone marked in red. It's worth reading the actual number, not just the needle's approximate position.
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