Oiginal Presidium Gem Gemstone Diamond Duo Tester (PDT) without Simulant Stones Presidium DuoTester (PDT) The only gemological instrument in the industry that tests gemstones using both thermal and reflectivity testing. Presidium DuoTester is the only comprehensive tool on the market that combines two proven testing methods for gemstones. PDT differentiates diamonds from its simulants based on both their thermal conductivity and reflective indexes. Coated gemstones can also be generally tested with the PDT, The Presidium DuoTester has a retractable probe tip that ensures consistent pressure against the gemstone during testing for more reliable results. With the industrys thinnest probe tip size of 0.6mm, PDT tests gemstones as small as 0.02ct.