This machine is a simple device for doing addition and subtraction mechanically.
Before the invention of electronic calculators in the middle of the 20th century, the only way of doing complicated sums, other than on paper, was to use some sort of mechanical device. The abacus is the simplest mechanical device for doing arithmetic. It was invented at least 5000 years ago and is still in use today, mainly in China and other parts of the Far East.
© Museum of the History of Science, Oxford
In Europe from the 15th century, more sophisticated mechanical calculators began to be invented. Leonardo da Vinci drew several different designs for machines made of cogs, pulleys and weights to do calculations. However, it is unlikely than any of these were actually made. In the 17th century the famous French mathematician Pascal designed one of the first mechanical calculators that worked successfully, but it was expensive and difficult to manufacture.
In the late 17th century and the 18th century in England, engineers and men of science designed simple, cheap, small and reliable calculating machines, such as this one. It is made out of wood, with ivory indicator dials. Inside, the hidden mechanism is made of steel cogs.
To use the machine, you turn one of the circular dials by putting the end of a pencil or a pin in one of the small holes on its rim. One complete turn of the dial causes the next dial up in the sequence to move on one digit. Turning the dial the other way causes the next dial up to move back one digit. Note that the numbers on some dials increase anticlockwise while on other dials they increase clockwise, so you have to be careful. This is due to the simple design of the mechanism inside.
The dials are labelled HM for hundred millions, 'XM' for ten millions, 'M' for millions, 'HT' for hundred thousands, 'XT' for ten thousands, 'T' for thousands, 'H' for hundreds, and 'X' for tens. Then comes 'L' for pounds, 'S' for shillings, 'D' for pence and 'F' for farthings. This is the old system of money used until 1971.
The machine is called a Stanhope adding machine because it was invented by Charles Stanhope. Charles Stanhope was a famous inventor in the 18th century and a fellow of the Royal Society in London - a place where the best scientists used to meet. He also invented more complicated calculating machines, as well as a special kind of printing press and a device for tuning musical instruments. Historians say that he was a tall and thin man, who looked pale, but he had a very powerful voice and used to wave his arms around a lot when he was explaining things.
Despite carrying out a very simple task, mechanical adding machines similar to this one were very widely used in the past, especially by people who had to do lots of addition, such as shop owners and bankers.