I use the redding competition shellholder sets . it's the easiest way to make small consistent adjustments .
or for measuring this ; if you have a dial indicator use it with a magnetic base . set up on top of your press with the dial ind. stem on the die top . zero the dial ind. turning the die , up or down , can be measured with the dial ind. you don't need a million dollar dial ind. , and magnetic base for this . an econo one with a 1" travel would be ideal . there was a couple dial ind. for sale on the forum , I can't remember what they were .