mm′
nn′ = (πD)/(πd),

or otherwise

mm′ = 3.1416 D,

and

nn′ = 3.1416 d.

We have also,

mm′
nn′ = mo
no.

Expressing the radius of curvature by r, and the half gauge by e, the above proportion may be expressed by

mm′
nn′ = r + e
re,

and also