In reply to rotsoscooper:
stand up straight next to a wall, mark your height!
measure your arm span from floor to that mark!
if your an average male your arm span will be identical to your height mark.
every inch passed the mark you can reach is a +1 and visa versa if you can't reach the mark. So for example im -1 as my arms are 1 inch short of the mark!
sorted?