706,807. Calculating-apparatus. SKOLMATERIELDISTRIBUTION AKTIEBOLAG. Nov. 21, 1951, No. 27301/51. Class 106 (1). [Also in Group XV] An adding and subtracting device comprises a lower plate 4 and an upper apertured plate 5, the plates being fixed to and covering each other, and two additional superposed plates 7 and 8 disposed between the plates 4 and 5, the plates 7 and 8 having different surface appearances and being movable to expose the plate 4 through one at a time of the apertures 6 in the plate 5, the plate 4 having a different surface appearance from the other plates so that when the plates 7 and 8 are moved relatively to each other and to plates 4 and 5 the apertures 6 from which plate 5 is withdrawn are divided into two groups of different appearance, a scale 3 being combined with the plates for reading the sum of the apertures of the two groups. Plates 7 and 8 and a covering layer 15 on plate 4 may be differently coloured or patterned. Plates 7 and 8 are shaped as at 12, 13 so that they may be positioned by means of members 9 and 10 so as to expose odd or even numbers ; thus Fig. 1 illustrates the addition 5 + 8. Adjacent to rail 1 the plate 5 is provided with a slot 14 through which the edges of plates 7 and 8 are visible, and layer 15 and plate 7 may be provided with scales which appear in slot 14. The device may be constructed in the form of a rule, and the holes 6 may be divided into groups by lines 16.
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