Ina hardness test, L is load in kg, D is diameter of ball in mm and d is diameter of indentation in mm. Brinell Hardness Numberis expressed by the equation

A

$$BHN = \frac {L}{\pi D(D - \sqrt{D^2 - d^2})}$$

B

$$BHN = \frac {2L}{\pi D(D - \sqrt{D^2 - d^2})}$$

C

$$BHN = \frac {L}{\pi d(D - \sqrt{D^2 - d^2})}$$

D

$$BHN = \frac {2L}{\pi d(D - \sqrt{D^2 - d^2})}$$