t oz:

A troy ounce (t oz) or (toz) is a unit of measure used for weighing precious metals that dates back to the Middle Ages.
Originally used in Troyes, France, one troy ounce is equal to 31.21 grams, according to the U.K. Royal Mint.


g:

The gram (alternative spelling: gramme; SI unit symbol: g) (Latin gramma, from Greek γράμμα, grámma) is a metric system unit of mass.
Originally defined as "the absolute weight of a volume of pure water equal to the cube of the hundredth part of a metre [1 cm3], and at the temperature of melting ice" (later at 4 °C, the temperature of maximum density of water).
However, in a reversal of reference and defined units, a gram is now defined as one thousandth of the SI base unit, the kilogram, or 1×10−3 kg, which itself is now defined by the International Bureau of Weights and Measures, not in terms of grams, but by "the amount of electricity needed to counteract its force".



By the way, this app is useful for converting amounts from Gram to Troy Ounce and vise verse.