The drawings and data sheets are, keyed using the following system:

(1) The first number denotes the caliber of the shell, the letter denotes the type (HE, AP, etc. and the last number denotes the number of the shell in its particular series.

(2) Thus 75-A-1 mean a 7 cm high explosive shell which is number one in its own series.

This system is used to enable additional sheets to be inserted in correct position.