The mean diameter of armour is calculated as the mean value between the mean diameter of the first armour layer and the mean diameter of the second armour layer.

Symbol
$d_{\mathrm{a}}$
Unit
mm
Formulae
$\frac{D_{\mathrm{2_{\mathrm{1}}}}}{2} + \frac{d_{\mathrm{a_{\mathrm{2}}}}}{2} + \frac{d_{\mathrm{f_{\mathrm{2}}}}}{2}$
Related
$D_{\mathrm{2_{\mathrm{1}}}}$
$d_{\mathrm{a_{\mathrm{2}}}}$
$d_{\mathrm{f_{\mathrm{2}}}}$
Used in
$d_{\mathrm{e}}$
$\delta$
$F_{\mathrm{e}}$
$\lambda_{\mathrm{2}}$