Kingson pocket calculator incorporating 2 x 6 bank registers manufactured in aluminium and steel (c.1965). A stylus is clipped to the side and there is a PVC protective sleeve.
It is a 6-decade “Addiator” type calculator for use with totals up to 999,999 and is operated by the pointed stylus. Pulling the bar at the top resets all digits to zero. The first number is entered by placing the stylus into the tooth indicated by the digit scale and pulling downwards; the digit will then show in the central window. To add another number, the same process is used, except that if the appropriate tooth for the new digit is red, then the stylus must be moved upwards, around the loop at the top, and down the other side to carry one into the next highest digit. If the next highest digit is already a 9, then a carry into it will show in the window as an arrow pointing upwards. When this occurs, the stylus must be placed in the 0 tooth for that digit and moved right up and around to carry one into the next digit. If you try to add 1 to say 199999 then you will have to do this four times before the result shows as 200000 (successively: 199999 – 1999’0 – 199’00 – 19’000 – 1’0000 – 200000).
Subtraction is much the same except that the lower set of teeth are used, movement is upwards for white teeth and downwards for red, carry involves going right to the bottom and back up again, and overflow shows as a downwards arrow corrected by a full downwards movement. (See http://www.caffnib.co.uk/calculators/calculators.html.)