Constant UPSTREAM_PPM_SCALE 

const UPSTREAM_PPM_SCALE: f64 = _; // 0.26752212800000003f64

Upstream expresses its mask thresholds per unit of phase / (TE[ms] · B₀[T]). One ppm of field is γ · 1e-3 · 1e-6 of that, so dividing an upstream threshold by this constant converts it to ppm.