## Circular pitch
$P_c$ is the arc distance between two adjacent teeth. The pitch diameter is used for calculating the distance between the centers of gears.

Center distance:
$$c = {d_1 + d_2 \over 2} = {(N_1 + N_2)m \over 2}$$

Diametral pitch:
$$P = {N \over d}$$
Where:
- $N$ is the number of teeth

Module:
$$m = {d \over N}$$