AS A GEM GAUGE
You might think to yourself: rather than measure a stone, look up charts and formulae, then use a calculator to work out the weight - can't this all be done automatically, with a computer built into the gauge??
The answer is yes. Select the stone on the display, measure it, the weight will be displayed. This is the top model of gauge from the best manufacturers of electronic gem testing equipment.
AS A GEM TESTER
Weigh the stone very accurately on a weighing machine, measure it, the built-in computer will calculate it's specific gravity (SG) and give a suggestion as to what the stone might be. This is not a 'guaranteed' method of identifying gemstones, since many gemstones have similar SGs, but it's useful guide.
These are the stones listed, whether you use this as a measuring gauge to see the size (weight) of a stone, or whether you weigh the stone and get the computer to suggest its identity:
Albite feldspar, Alexandrite, Amber, Andradite garnet, Apatite
Benitoite, Beryl, Brazillianite
Calcite, Chalcedony, Coral, Corundum, Cubic zirconium oxide
Danburite, Diamond, Diopside, Dipotase
Malachite, Microline, Moissanite, Moldavite
Obsidian, Oligoclase feldspar
Pearl, Peridot, Plastic, Pyrope garnet
Rhodochrosite, Rhodolite garnet, Rhodonite
Sapphire, Scapolite, Serpentine, Shell, Sinhalite, Sodalite, Spessartite garnet, Sphene, Spinel, Spodumene ,Strontium titanate, Synthetic emerald, Synthetic rutile, Synthetic spinel
TL grossularite garnet, Turquoise
Zircon (high), Zircon (low), Zircon (medium), Zoisite