Troy ounce, grams or grains???

[Russ Nobbs]

31.1 grams per troy ounce

"Jeweler's Resource" says it's 28.3 grams per avoirdupois ounce. (Hmmmm, I think I've used 28.8 grams per  av.  ounce in the past.... I'd better double check my charts...Maybe I always use it wrong?)

Pennyweights (dwt's), Grains and Carats are the other, less common, measurements used in jewelry.

1 grain = .0648 grams
1 dwt's = 1.5552 grams
1 dwt's = .05 troy ounces (or 20 dwt's per troy ounce)
1 Carat = .2 grams (or 5 grams per Carat)

It would be simpler if we just used grams for everything, eh?

Here's a link to a downloadable conversion program for mass: http://www.downlinx.com/proghtml/346/34646.htm
that I found with a search on the web

[Metalfairy]

What is meant by Troy Ounce.  I see this used in silver and gold metals all the time.  How does this transfer to the gram weight used with ACS?  Where does this come from and when was it started?  What is the difference in a troy ounce and regular ounce?  This subject has me befuddled - a little.