the depth changes,,, all mrk 1 ferret boxes are 15 foot in reality,,its just the stiker on the depth gauge, and the the 15 foot collar.
your 8 foot collar will register 15 foot on your 15 foot box,,,, but it will only be 8 foot...deep... is this clear to you
no im still confused, so i dont just use the 15ft box up to 8 foot