Measure the diamond horizontally and vertically, look up the measurements in the little book to see the weight, cleverly designed for different shapes not just rounds.
Also included, a chart listing 16 gemstones and a formula. You measure the stone in mm, find yourself a calculator and follow the formula to calculate the weight.
This is the only gauge that can be switched to carat (usually you can only measure in millimetres and must convert it); the only gauge I have seen that has an extra attachment for inserting into small items of jewellery.
Other features: clever power system, to turn it off you simply put the gauge back in its case - and that protects it - it is an exceptionally accurate and sensitive instrument.
Brand: Presidium (the leaders in gem equipment), made in Singapore
Range: 0.01mm to 25.00mm
Readings: ± 0.01mm (i.e. to allow for a reading is being rounded up or down).
Accuracy: maximum error 0.02mm when measuring 25mm. For small measurements (i.e. most diamonds and gemstones) the error would be nominal.
Units: switchable to millimetres or carats
Cuts: it will 'weigh': rounds (brilliants), marquise, square, baguette, emerald-shape, pearl shape.
Power: one CR2032 battery (lasts 16 hours of continuous use). Auto-power-off if not used in 10mns.
Measuring modes (mechanical): with the 'points' for loose stones and most mounted stones; with jewellery attachment for tiny mounts; with the 'wedge' for measuring the insides of holes (e.g. rub-over settings).