A binary adding machine created with D. Moews' program - see thing:2425746 - "A Slide Adder". The program is available for download at http://djm.cc/slide-adder-0.03.zip. A feature of the program is that one can choose the base of the number system; here base 2 was used. The machine has six digits and overflows if sums greater that 63 occur. However it might be useful for instruction. An exercise is to add 7, (binary 111), 9 times. If properly done the result will be 111111, (decimal 63).
To set the adder to zero tap the top gently on a surface moving the sliders so that the windows all show "0". To add a number work from right to left. If "0" is to be added skip the column. If "1" is to be added look to its left. If a triangular hole is present use a stylus to pull the hole to the bottom stop. If a slot is present use the stylus to push the slot up and then over the curve to the stop.
After addition, right to left, is completed "+" signs may occur in some windows. The "+" signs can be cleared as follows; again move from right to left. Add "0" to the columns containing a "+" sign by moving the slot next to the "0" up and then over the curve to the stop. Repeat the process as necessary. The "+" sign cannot be removed from column 32; overflow has occurred.