If you can' t find your arrows the best and easiest way to measure for new ones is to take your bow to the shop and nock a new arrow and then the pro shop guy can mark them and cut them to length.

AS far as the numbers on the box goes, that simply means that the arrows are full length and uncut (31 inches) and are spined to be shot out of a 60 - 70 pound bow. Generally speaking. That spine rating will change however the shorter you cut them and the heavier or lighter weight tip that you use.

Your pro shop will be able to help you out with " hands on" instruction.