 A homespun example from the 18th century illustrates this point nicely: the efforts of the English potter Josiah Wedgwood (1730–1795) to extend the temperature scale to cover the very high temperatures in his kilns, at which mercury vaporized and glass melted. All previously known thermometers failed in that pyrometric range, so Wedgwood felt obliged to invent a whole new measurement standard (reminiscent of Bridgman in his high-pressure laboratory). Wedgwood noticed that very high temperatures made pieces of clay shrink, and created a temperature scale by assuming that the amount of contraction was proportional to temperature beyond “red heat”. As the start of his scale (red heat, defined as 0) was already beyond the boiling point of mercury, Wedgwood’s scale was wholly disconnected from the temperature scale defined by mercury thermometers. Later, in response to widespread demand to clarify the meaning of his scale in more usual terms, Wedgwood made a translation of his scale into Fahrenheit degrees, by means of an intermediate standard (thermal expansion of silver) which overlapped with the high end of the mercury scale and the low end of the clay scale. (This procedure produced some unlikely numbers, for example 21,877°F for the temperature of his air-furnace.) It seems that Wedgwood initially did exactly what operationalist conscience would dictate: as the new instrument did not operate at all in the range of any trustworthy previous thermometers, he made a fresh scale. Why was that not the honest thing to do, and quite sufficient, too? Why did everyone, including Wedgwood himself, feel compelled to interpret the Wedgwood clay scale in terms of the Fahrenheit mercury scale? Why was a continuous extension desired so strongly, when a disjointed set of operations seemed to serve all necessary practical purposes?