Or a surface plate (or any flat reference) and jig to transfer dial indicator measurements. I could use the same jig I made for measuring parallelism of my jointer infeed and outfeed tables.
Shim the reference surface so that a 3 point plane is coplanar between the reference plate and milled wasteboard, then take measurements with the dial indicator. The jig slides on 3 sharp points on the base and with careful operation is quite precise.
It’s not precise to microns like a CMM, but it can read precisely to about half a thou.