Accession No

6155

Brief Description

Exactus stylus mechanical adding machine, 1950s/60s

Origin

England

Maker

Exactus Business Machines

Class

calculating

Earliest Date

1950

Latest Date

1969

Inscription Date

Material

Metal; plastic; paper

Dimensions

Special Collection

Hookham collection

Provenance

Donated on or before 08/08/2007.

Inscription

‘EXACTUS
TRADE MARK’ (top of adding machine)
‘MINI-ADD
MADE IN ENGLAND’ (bottom of adding machine)

Description Notes

Mechanical adding machine with painted tin front plate, 1950s-1960s.
Black plastic case opens like a book, with calculator able to slot under strip of plastic on one side and an instruction booklet able to slot into a plastic pocket on the other side, on the inside of the case.

Nine holes at the top reveal the result of the calculation with places for shillings and pence. Beneath these are four columns for entering pounds, two for entering shillings and two for entering pennies and farthings. A hinged plate allows the columns to read for addition or subtraction. Toothed scale (partially painted red) which can move to adjust the number in the window. Metal bar at top for clearing numbers. Other side of the calculator has the same layout but is used for subtraction.
White metal stylus, by which to operate the calculator, is stored at side of instrument.

Good/fair condition.

References

Events

Description
Flipping the hinged plate between its upper and lower positions changes the mode between subtraction and addition by changing the direction of numebrs displayed.

To add (eg) 5, the operator inserts a metal stylus in the hole to the right of the number and pulls the slide down to the bottom. The result appears in the circular window above.

Numbers appearing in the clear portion of the slide can be added directly by the same method. Numbers appearing in the red section can not be added directly, as the slide only has 10 positions and will not move far enough down. The addition has to be performed by subtracting the complement of the number and adding ten in the next column. Although this sounds complicated, it is mechanised by a simple process of inserting the stylus opposite the required number (eg 7), moving the slide up to the top of the slot (thus subtracting 3), "around the bend" to engage with the slide in the next column, and back down the short slot to the end (thus adding 1 in the "tens" column). The result (5 - 3 + 10 = 12) appears in the windows. Note that the openings in the red section are slots rather than holes, to allow the stylus to move sideways.

FM:46618