Constant GEODESIC_MAX_FLATTENING 

pub const GEODESIC_MAX_FLATTENING: f64 = _; // 0.0066666666666666671f64

The largest flattening the geodesics accept, 1/150: Karney 2013 (page 9) shows the sixth-order series’ truncation below f64 round-off up to there. GeographicLib’s own error table for the series grows to 10 µm at f = 0.05 and 0.3 m at 0.2. Every planet-like body hpr flies on is inside: WGS 84’s f is 1/298.257.