The Add-A-Time and other unusual addiators

Until the appearance of electronic pocket calculators in the mid 1970s many people bought mechanical pocket calculators such as the one below.  These did base 10 addition and subtraction.  I suspect that they were not much faster than pencil and paper or mental arithmetic for most calculations.

Perhaps the people who bought them were seduced by advertising that claimed that they also did multiplication and division. Like much advertising this was true but misleading. The addiator could multiply, but only by repeated addition. It could divide, but only by repeated subtraction.Slide rules, log tables and ready reckoners worked much better than addiators for multiplication and division.

Some specialised addiators might have been more useful. For example, the Add-A-Time added minutes and hours.

Until decimalisation in 1971 the British Pound was divided into twenty shillings and each shilling into twelve pence [and each penny into four farthings]. Mental arithmetic was tricky. Ready reckoner books of tables were used for commercial calculations [17 widgets at £3/16/8 each] but  the following addiator would have been quicker than mental arithmetic for addition and subtraction.

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