Ade Advanced Optics Digital/electronic Gem Refractometer 1.4~3.0 Ri Gemological Gemstone Diamond Jewel Testing Tool No refractometer oil needed, Read instant results on LCD Wide measuring range: 1.400 ~ 3.000 RI, High accuracy:  0.007 RI separate diamonds, moissanites and other colored gemstones via its Refractive Index Item weight: approx. 339g. Item size: approx. 105 x 60 x 35 mm Power source: 1 x 9V battery. Working temperature: 10 ~ 28C (50 ~ 82.4F). Gemstone must have a at lease 0.11 inch (3mm) well polished flat surface for accurate result