It can be measured fairly accurately with a caliper however I like to use feeler gauges. You can by a set an any auto parts store for under 10.00 and always be positive about girdle thickness. I hope this helps and good luck with the 2018 entry. Large facets with exacting meetpoints can be lost during polishing. be careful with your polishing to maintain those meetpoints. pay attention to where they say to take your measurements from. And always get your girdle with enough width for mounting the stone. Mounting puts pressure on those edges and your girdle width must be strong enough to not crack under pressure.