Resulta BS-7

The three main components laid out. Removing four screws allows the cover-plate to be taken off, undoing the two nuts under the machine allows the baseplate to be taken off.

The main frame of the little adding machine is riveted together, so cannot easily be taken apart. Nevertheless, with the baseplate and cover off, much of the dust and dirt it has accumulated since January 1939 can be brushed away. The mechanism internally is dominated by the large wheels and segments used to enter a number, adding the number of digits to the totals-register as they are being pulled down.

The view from the bottom into the mechanism shows the long springs that pull the segments back to zero (left) and the input-check register can be seen (right) with the row of detent-levers that hold the number after setting. Pressing down the 'space-bar' at the front tilts these levers, releasing the segments to zip back to their zero position.

Assembled again and cleaned-up - it does like a little like a miniature cash-register. It is a bit similar; it is a little adding machine. The Resulta adding-machines were manufactured in Berlin from 1927 into the 1960s at least. All machines have a number scratched into the base, showing the month and year of manufacture (plus the letter or initials of the person doing the quality-check). This specimen has the code 139g - so checked in January 1939 by employee 'G'.

This specimen is not quite original, as somebody in the past tried to polish-up the aluminium cover, removing the beige-grey finish and dulling the black outlines. Nevertheless, even in shiny aluminium with the now light-grey outlines it still looks ok and after a bit of practice works fine.

Just like typewriters, the rubber feet have decayed and the machine settled down on the rim of the metal base. The simple fix was to 'sole' the feet. Fitting rings were punched from felt-sheet (the felt sold for putting under furniture, it is very tight and can handle mechanical load). A few drops of latex-rubber (textile glue) and spraying with Plasti-Dip gives these new soles a good grip - glued into place on the old, hard rubber feet.

Another thing is the stylus - that is often missing with these calculators. Browsing the internet gave information on what the original stylus probably looked like. The post-war calculators seem to have had a green, shaped, double-ended stylus - the 1930s specimens probably had a simpler, black stylus. From an old pencil and a suitable nail a credible reproduction stylus was crafted.

Cleaned and now with a stylus, the Resulta BS-7 calculator works fine. It is a basic adding machine, with subtraction too. It does have a feature for quick-repeat adding to do multiplication, but I would not characterise this as a four-species calculator.

In the picture above, 12.75 was entered and the input cleared. Then 7.95 was added; the 7.95 showing in the lower input check-register. The sum is shown in the top totals-register. The crank at the top-right clears the totals register again. The lever at the left shifts the machine into subtraction-mode. 

There is a lot of information and a very clear video explaining the machine's workings on this collector's site.

A fun little (and surprisingly heavy) addition to the small set of vintage calculating tools :-)