Pushrod measuring issue

I just did the rocker arm geometry on my 340.
Harbor freight has a nice 8 inch dial caliper for about $25.00 or less. Its good enough.
You must use a 5/16 ball in the cup for measurement of push rods as each brand of cup is different. Total length does NOT work for this measurement! the ball is at most hardware stores in the nut and bolt dept. The 5/16 ball measures .3125
use 1/2 this measurement .1563 to get total length.
While checking this use zero valve lash to eliminate one more possible mistake.
Donnie