TC25-261 PLAIN SCALE. Belcher Brothers. Plain scales were invented around 1750, and included a variety of scales (sine, etc.) that could be used with a pair of dividers to solve trigonometric functions. This one is unusual both by being American (most were English) and by being 24" (most were 12"). Boxwood with inset brass plugs to protect the wood from divider points. Wood worn and darkened but markings clear. Good 120-240