What does "trones" mean?

Trones: A form of weighing machine for heavy wares, consisting of two horizontal bars crossing each other, beaked at the extremities, and supported by a wooden pillar. It is now mostly disused. [Scot.] Jamieson. Trone stone, a weight equivalent to nineteen and a half pounds. [Scot.] -- Trone weight, a weight formerly used in Scotland, in which a pound varied from 21 to 28 ounces avoirdupois.