The equivaent thickness of armour is based on the combined thickness of the first and second armour layer divided by the mean diameter of the first and second armour layer diameter. The error to a separately calculated value for each layer is not significant since the electrical resistance is calculated separately.

$\delta $

mm

$\frac{A_{\mathrm{a}}}{d_{\mathrm{a}} \pi}$

$d_{\mathrm{a}}$

$\pi$

$\lambda_{\mathrm{2}}$