I made an assortment of acrylic step gauges with 1/2 mm steps. I find “best focus” for a given lens and then mark the correct step with a sharpie. It makes it easy to adjust focus and to “subtract” focus height for thick materials.
Here’s a lbrn file for a couple of the ones I made.
focus gauge 10a.lbrn (219.1 KB)
Pro TIp: Make them out of brightly colored acrylic instead of clear, because when you lay the clear ones down they “hide” and play hard to find.