For measuring the top-to-bottom of a stone, the gauge has two fine prongs. These are 1.5mm diameter. So you must be able to insert a 1.5mm prong underneath the setting in order to measure the stone.
With our instructions you can calculate the weight of diamond, alexandrite, amethyst, aquamarine (beryl), tourmaline, chrysoberyl, chrsoprase, citrine, garnet, opal, peridot, quartz, ruby and sapphire (corundum), spinel, topaz, tourmaline and zircon.