avoirdupois weight

Try this on for size: A diamond that weighs over a pound!
Try this on for size: A diamond that weighs over a pound!

If you’re like me, sometimes weights and measures are confusing.  For example, I have trouble remembering if a pound has 16 or 12 ounces.  Different weight systems devised by medieval traders are the source of the confusion.

It all depends on what you’re measuring.  For most goods (avoir de pois means “goods of weight”), 16 ounces equals 1 pound.  However, If you’re measuring precious metals, you need to use troy weight, and 12 ounces is a pound there.  Since apothecaries’ weights (for pharmaceuticals) are no longer used, it’s the troy weights that are the source of confusion for me.

And, in case you wondered, diamonds have their own weight measure, the carat.  Wolframalpha.com calculates that it takes 2268 carats to make a pound.  According to Wikipedia, the South African Cullinan diamond, the largest gem-quality diamond ever found, weighs in at 3106.75 carat (621.35 g, 1.37 lb).

Photo credit: http://bit.ly/1HmKCTD

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