In the school museum I came across two very simple pen-based computing aids. The devices are very simple mechanical tools that help to do addition and subtraction. It was called ADDIATOR. The utility is limited to addition and subtraction and it provides a very simple mechanism to deal with carry-over. If the number which is to be moved is white the calculation is without carry-over and one pulls it down. If the number is red then there will be a carry over one has to pull up and around the semi-circle (this is the mechanism for carry over). A carry over beyond the next position is displayed with a special sign and has to be resolved by moving the next position. The curator told me that he remembers people in shops used them and that people where very quick with them. It seems they have been popular till I was born.
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