Plate calipers from the big guys are $125+, and pretty simple apparatus - why not DIY.
Out in the shop there were some aluminum extrusions that I've been saving for years - unable to part with them, knowing some day they would be useful. The day arrived. In about 20 minutes I knocked together a thickness caliper with a $10 HF dial gauge and a few pieces of the extrusion and connectors. Opposite the dial gauge is a leather pool cue tip I found - should help isolate the thickness reading while protecting the top/back from any damage.
HF Dial Indicator - use your coupon!
http://www.harborfreight.com/1-inch-tra ... r-623.html
I've seen these built with MDF frames as well - the aluminum extrusions are overkill, but was quick and easy as they were on hand.
(I didn't cut any aluminum on the table saw - just used it as a square surface for assembly)

