Learn about new technologies! 
In a Hartnell governor, the stiffness of the spring is given by (where S1 and S2 = Spring forces exerted on the sleeve at max. and min. radii of rotation, and h = Compression of the spring)
(S₁ + S₂)/h
(S₁ - S₂)/h
(S₁ + S₂)/2h
(S₁ - S₂)/2h