I am taking a gemology course online and now need to buy a refractometer to continue and be able to test gems I buy from sellers outside of the well known, respected sources(not that they are shysters, just small time sellers or ones oversees in Indian, for example). I am working(slowly as I can afford things)on starting a little home business to supplement my disability income making some jewelry and selling some gems. I have been looking at the Presidium II that measures RI from 1-3., conveniently spitting out your RI number on a screen and then another one (the name escapes me at the moment) that tells you on screen what the gem is! Yes, they are several hundred dollars, compared to less than $100. for a traditional refractometer, but seems great convenience as I buy parcels.. I do realize the digital doesn't work on cabachons, but I rarely deal with those. Money is very tight for me, so keep in mind that it's not like I have lots of extra for what may be frivolous purchases. I welcome any input, comments or good resources to buy what may be recommended.