Constant STANDARD_GRAVITY_MPS2 

pub const STANDARD_GRAVITY_MPS2: f64 = 9.806_65;

Standard acceleration of free fall, g₀ = 9.80665 m/s²: the conventional value adopted by the 3rd CGPM (1901) and used by the U.S. Standard Atmosphere, 1976. It is not the gravity at any particular place.