checking compression ratio

Yes, that would be a bit tricky to do. Getting the air out of the pocket at the top is the problem.

If you have that head gasket PN, that would help zero in the numbers. The computed numbers are pretty close... close enough to reliably pick a cam for instance.

But if you have many mods to the head, like milled or chambers polished or some valve work, then it can run the computed numbers off several tenths; in your setup, the SCR varies a bit over 1 tenth of a point for each cc.