This is an instrument that is used to measure a diamond's length, width and depth in millimeters. A diamond must be specifically measured as experts compare the measurements to the diamond’s weight in carat. An 0.50ct round diamond for example has a diameter of around 5.2mm and a 1.00ct round diamond’s diameter is around 6.5mm. When working with diamonds lighter than 0.30ct, people generally refer to the diamond’s size in millimeter rather than their weight in carat. Precise measurements are of the utmost importance in the diamond industry to ensure high quality standards are maintained.