I am gonna jump back in here:
"Measure with a depth gage of your choice". That's the issue IMO. Failproof? I don't think so. What is that magical gage that can measure a clay indent on a piston?
I tried that method a long time ago. I ended up with a bunch of pie slices I could not get a consistent reading on no matter how many times I tried. I thought those slices were important to me and so they stayed in my parts bin for many years. I recently threw them out.
I'll continue to use the dial indicator method and if I am close, I'll feel better knowing I may have 0.025 or so more clearance than I am measuring.