The stiffness of the spring in a hartnell governor is equal to $$S_{1}$$ = Spring force exerted on the slleve at maximum radius of rotation $$S_{2}$$= Spring force exerted on the slleve at minimum radius of rotation

A

$$\frac{2(S_{1--} - S_{2})}{h}$$

B

$$\frac{S_{1--} - S_{2}}{2h}$$

C

$$\frac{S_{1--} + S_{2}}{h}$$

D

$$\frac{S_{1--} - S_{2}}{h}$$