What I come up with as a fixed point on the farme is the spring bolts, so took that point to the inner bead. This is what I come up doing that, used the inner most face. I was having trouble with the two rear bead measurements, could had got that one wrong but came up with close to the same thing twice. This is the dial indicator I have. Im going to have to look aroung for a better means to support, best I could come up with is a bit sketch at best.