Stereotype and mould, from the Scheutz Difference Engine No 3, 1859.
© Science Museum / Science & Society Picture Library
This was a means of eliminating errors of calculation, transcription and printing, by producing multiple copies when printing log tables. Father and son, George and Edvard Scheutz, built a Difference Engine, based on the ideas of British computing pioneer Charles Babbage, with the numbers impresed into papier mache or metal strips. These were then used as moulds from which multiple copies of the results could be printed.