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One troy pound is 12 ounces.
Literal
Troy-pound 1-pound [topic-は] 12-ounces is-[copula-である].
A technical measurement definition. 金衡 ('troy weight') is the traditional weight system used for precious metals — 'troy' comes from the French city Troyes. である is the formal copula used in definitions. A specialized piece of jewelry/metallurgy knowledge rendered in terse Japanese.