pub const GRAMS_PER_GRAIN: f64 = 0.06479891;Expand description
Grams per grain — exact by definition.
The international avoirdupois pound is defined as exactly 0.45359237 kg (i.e. 453.59237 g), and one pound is exactly 7000 grains, so this value is exact (not a measured or rounded conversion): 453.59237 g / 7000 = 0.06479891 g/grain (equivalently, 0.45359237 kg / 7000 = 0.00006479891 kg/grain, then x1000 to get grams).
This is the single source of truth for the grain<->gram conversion; do
not re-derive or re-round it elsewhere (see tests/constants_guard.rs).