GCAL, located in the World Diamond Tower in New York city is an independent diamond and gemstone certification laboratory. GCAL is the only diamond grading laboratory … •that provides a “Zero Tolerance” 4C’s Consumer Grading Guarantee •that includes Gemprint® Security Registration with every certificate •that includes Diamond Profile® light performance analysis •that is ISO 17025 accredited in North America •that weighs, measures, examines, tests, analyzes and photographs every diamond several times