Standard Electronic Gem Tester (Presidium PGT II) Resolution_1g the sensor must be kept

the sensor must be kept dust-free

a watchmaker's eyeglass and a good quality spring lug remover too - all in a fitted case

Not diamond (and not Moissanite)

you missed the stone and touched the setting)

Works with any stone

Standard Electronic Gem Tester (Presidium PGT II) Resolution_1g the sensor must be keptDETAILS Thermal meter, tests for 17 common groups of gemstones (about 40 varieties), enlarge the product picture to see the scale in detail. Works with any stone, loose or mounted in jewellery, even uncut stones. The only condition is that the stone (and tester) must be at room temperature. Instruction manual (pdf download) Video (youtube demonstration) Video (youtube calibration for serial numbers PTG111425 and after. Guide to buying electronic gem