A note on Regnault's innovative graph drawing (1847)

Regnault's tables of the thermodynamic properties of steam and other data w ere standard during much of the 19th century. To calculate them from the ex perimental measurements, he used a graphical method to distinguish between random and systematic errors, when both were so small that he had to plot p oints with an accuracy of one-hundredth of a millimetre. He did this on a l arge copper plate and did the curve fitting on the plate. This episode is s et against the development of the drawing of experimental graphs from the m id-18th century onwards.