# Mean diameter of armour

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
$d_{a}$
Unit
mm
Formulae
$\frac{d_{a_{1}}}{2} + \frac{d_{a_{2}}}{2}$
Related
$d_{a_{1}}$
$d_{a_{2}}$
Used in
$d_{e}$
$\delta _{ar}$