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.


lb:

Pound, unit of avoirdupois weight, equal to 16 ounces, 7,000 grains, or 0.45359237 kg, and of troy and apothecaries' weight, equal to 12 ounces, 5,760 grains, or 0.3732417216 kg. The Roman ancestor of the modern pound, the libra, is the source of the abbreviation lb.
The pound or pound-mass is a unit of mass used in the imperial, United States customary and other systems of measurement.
Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.45359237 kilograms, and which is divided into 16 avoirdupois ounces.
The international standard symbol for the avoirdupois pound is lb; an alternative symbol is lbm (for most pound definitions), # (chiefly in the U.S.), and ℔ or ″̶ (specifically for the apothecaries' pound).



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