Canadian Military measurements for foot wear is calculated as follows.
The first set of numbers represents the length (in mm) of your foot from the very back of the heal to the tip of the big toe (Red Line A).
The second set of numbers represents the width (in mm) of your foot at the widest point just bellow the start of your toes (Black Line B).
Shoe size 252/92 would fit a person with a 252mm Heal to Big Toe Measurement and 92mm Measurement of the Widest part of the foot.
Most Army Surplus boots contain either a hole or cut in the tongue to signify the boot is a demilitarised product.