Constant ELECTROMAGNETISM_VACUUM_PERMEABILITY 

pub const ELECTROMAGNETISM_VACUUM_PERMEABILITY: f64 = 1.256_637_062_12e-6; // 1.2566370621199999E-6f64

Vacuum permeability in henries per meter.

This crate keeps the value locally as a convenience for scalar electromagnetic helpers. Broader physical constants belong in the top-level use-constants set.