Conventions

These rules apply to every function in the library.

Units

Everything is metric internally: bar, metres, litres, degrees Celsius and minutes. Imperial units exist only in the units module, at the edges.

Fractions

Gas fractions run from 0 to 1, never percent. A Gas is { fo2, fhe }; nitrogen (fn2) is always derived.

Gauge vs absolute

Pressures are gauge by default. Absolute parameters and returns have names ending in Abs, or are documented as absolute. Use gaugeToAbs to convert.

Water types

Depth math takes water: 'salt' | 'fresh', default 'salt'. Metres per bar are METERS_PER_BAR = { salt: 10, fresh: 10.3 }.

SURFACE_ATA vs ATM_BAR

Depth math uses SURFACE_ATA = 1 by default, overridable through an optional surfacePressure. Fill math uses ATM_BAR = 1.01325 for gauge to absolute conversion. They are different constants for different jobs.

AIR

AIR = { fo2: 0.209, fhe: 0 } is used everywhere, including presets.

Errors vs feasible

Impossible input (NaN, infinity, negative depth or volume, fractions out of range, fo2 + fhe > 1) throws a RangeError whose message names the parameter. A valid request with no solution is returned as data: feasible: false with a string-literal reason code. It is never thrown.

No rounding

The library never rounds, and it carries no UI copy. Round and word things at the edge.

useRealGas

Every function that can use real-gas behaviour takes useRealGas?: boolean inside its input object, defaulting to false. The compressibility factor Z is always evaluated at absolute pressure (see Real gas).

import { toBar, fromMeters } from 'dive-math/units'
import { ataAtDepth, gaugeToAbs } from 'dive-math/pressure'

toBar(3000, 'psi') // => 206.84
fromMeters(30, 'ft') // => 98.43
ataAtDepth(30.9, { water: 'fresh' }) // => 4
gaugeToAbs(0) // => 1.01325