Hello … Since I have taken the IGS practical exam on Gem Identification and passed it, I know how difficult it is. Before I was a Gemologist, I was a certified Metrologist (science of measurement for the military), so I’m real good with all kinds of measuring equipment. I have a Gem-n-Eye Digital Refractometer and find it is very good at detecting GLASS stones and also confirming when an RI is OTL (Over The Limit) of 1.81 on the standard refractometers. It is my learned opinion that you will have great difficulty in passing the IGS practical exam by only using a digital refractometer. However, it is very useful to have and use both types. 