Robertson's 'Rapid Calculator', c 1910.
© Science Museum / Science & Society Picture Library
Robertson's Rapid calculator, (patent no 5871) was made by the Robertson Rapid Calculator Company of Glasgow, this was one of several large-scale ready reckoners to be developed in the first decade of the 20th century. This form of ready reckoner placed the tables of numbers on four rollers, each one of which was likened to 'a book with 200 or 300 pages open at the one time'. It gave the cost of various quantities of goods at various prices per pound, hundredweight or ton.