A weighing scale or balance designed to oppose or check the accuracy of another scale, or a counterweight used in a balance system.
From counter- + scale. Scale comes from Old Norse skal meaning a bowl or cup (as in a balance). This commercial or scientific term relates to quality control and verification of measurements.
In ancient markets, merchants would have counterscales to verify that the seller's scale was honest—it's the original 'trust but verify' for commerce, and it's probably why we still distrust used car salesmen.
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