a balance or scale consisting of a metal arm suspended off center from above: the object to be weighed is hung from the shorter end, and a sliding weight is moved along the graduated longer end until the whole arm balances
See steelyard in American Heritage Dictionary 4
(stēlˈyärdˌ)
noun
A balance consisting of a scaled arm suspended off center, a hook at the shorter end on which to hang the object being weighed, and a counterbalance at the longer end that can be moved to find the weight.