Whatza Troy oz?  Not related to Helen's weight. 

Troy oz is (31.1035 grams/28.3495 grams) US oz = 1.0971446 US oz. (US oz = 1/16 US pound, which is 453.592 grams or .45392 kilogram and kilogram = 2.20462 US pounds =~ the mass of a liter of water.)

The standard on standards in US is NIST (just up 270), http://physics.nist.gov/cuu/Units/

Another annotated source has notes below:

http://www.unc.edu/~rowlett/units/dictT.html

troy weights

    a traditional English weight system of great antiquity, apparently in use since long before the Norman conquest of 1066. The system is believed to be named for the French market town of Troyes, where English merchants traded at least as early as the time of Charlemagne (early ninth century). The system is based on the troy pound [2] of 5760 grains. The pound was divided into 12 ounces (of 480 grains), each containing 20 pennyweight, with each pennyweight equal to 24 grains. Apothocaries, however, divided the troy ounce into 8 drams (of 60 grains), each containing 3 scruples, with each scruple equal to 20 grains. The origin of the troy system is not clear, but a number of scholars believe the dram corresponds to the denarius, a Roman coin that weighed about 60 English grains and (when used as a weight) was also divided into 3 scruples. The troy system was always the theoretical basis of the traditional English monetary system, in which there were 12 pence (pennies) to the shilling and 20 shillings to the pound. However, in medieval England pennies did not actually weigh a troy pennyweight, because they were made using the tower weight system (see above) and thus weighed 22.5 grains instead of 24. In 1527, Henry VIII abolished the tower pound and made the troy system official for coinage; thereafter silver shillings weighed exactly 0.6 troy ounce. The smaller troy weights continued in common use in pharmacy and monetary affairs into the early twentieth century, but the troy pound was abolished in 1878 to avoid any commercial confusion with the avoirdupois pound. The troy system is nearly obsolete today, but the prices of precious metals are still quoted by the troy ounce.

pound (lb t or lb or #) [2]

    a second traditional unit of mass or weight. The troy pound, named for the French market town of Troyes, was the unit used in England by apothecaries and jewelers. The troy pound is divided into 12 ounces like the Roman pound. One troy pound is 373.242 grams, or exactly 144/175 = 0.822 858 avoirdupois pounds (13.165 72 avoirdupois ounces). The troy and avoirdupois pounds are connected by the grain: there are 5760 grains in a troy pound and 7000 grains in an avoirdupois pound. See troy weights for additional information. The troy pound should be abbreviated lb. t. to distinguish it from the more common avoirdupois pound.

Troy oz is 373.242 grams/12 = 31.1035 grams

ounce (oz or oz av) [1]

    a traditional unit of weight. The avoirdupois ounce, the unit commonly used in the United States, is 1/16 pound or about 28.3495 grams. The avoirdupois ounce also equals 175/192 = about 0.911 457 troy ounce or 437.5 grains. The word ounce is from the Latin uncia, meaning a 1/12 part, because the Roman pound was divided into 12 ounces. The word "inch," meaning 1/12 foot, has the same root. The symbol oz is from the old Italian word onza (now spelled oncia) for an ounce. See avoirdupois weights for additional information.

Troy oz is (31.1035 grams/28.3495 grams) US oz = 1.0971446 US oz.