How diamonds are measured and weighed, diamond gauges, diamond balances (scales), phone app to measure diamonds
THE VALUE OF DIAMONDS
Diamonds are valued according to their clarity, colour and weight.
It is extremely rare for a diamond to be perfectly 'clean', it will have 'marks' (inclusions) inside. At worst, these will be visible to the naked eye; usually they are visible through a good quality 10X magnification jewellers loupe; for professional evaluation they need to be studied under a microscope. Clarity and colour grading requires training followed by a large amount of experience.
Diamonds are weighed in carats, often known as 'metric carats' not to be confused with carat (karat in the USA) as a measure of the purity of gold.
There are five carats in a gram and each carat is divided into 100 points. All weighing machines weigh in grams, some can also be switched to carats. When choosing a weighing machine, keep an eye on the decimal point. Most weighing machines weigh down to 0.1g (for weighing gold) - not good enough! Some weigh down to 0.01g = to the nearest 5 points. This is OK for weighing relatively low-value gemstones and for the approximate weighing of diamonds. It is better to go for a weighing machine that weighs down to 0.001g = to the nearest 0.5 point.
Since diamonds tend to be cut to standard dimensions, it is possible to measure the diameter of the top (table) and estimate the weight. These 'simple' diamond gauges are like very accurate knitting needle gauges. Prices range from £2.00 to £12.50.
There are various other types of diamond gauge: a gauge printed on micro-film, mounted onto a 10X loupe (dgi-loupe); or calipers for measuring the diameter and depth of a stone, you look up the two readings in a little book of charts (included) (DGX); or a digital micrometer with a built-in computer to calculate the weight of diamonds and other gemstones (DG-PRESID).
Estimating the weight by measuring the dimensions is never as accurate as actually weighing the stone.