Wedgwood scale

The Wedgwood scale (°W) is an obsolete temperature scale, which was used to measure temperatures above the boiling point of mercury of 356 °C (673 °F). The scale and associated measurement technique were proposed by the English potter Josiah Wedgwood in the 18th century. The measurement was based on the shrinking of clay when heated above red heat, and the shrinking was evaluated by comparing heated and unheated clay cylinders. It was the first standardised pyrometric device. The scale started at 1,077.5 °F (580.8 °C) being 0 °W and had 240 steps of 130 °F (72 °C). Both the origin and the step were later found inaccurate.