The machine contains: 3 bcd inverters, 2 bcd adders.,3 digit input, 3 digit output, and a negative indicator.
The machine supports negative numbers by using 10s complement on the output of the first BCD adder.
It requires another adder because negative numbers needs a +1 and normal adders would not work. So two BCD adders in total.
The inputs are in BCD digits meaning you can only input 0-9 in binary per digit. They are located east. Top inputs are A, bottom inputs are B. So for A+B you can do 0110 on the top inputs and then 0110 on the bottom to get 1100.
You can switch between addition and subtraction by using the two levers on the right (from facing west towards the machine). Each lever is used to control which input should become B in the equation "A+!B=A-B". With no inputs on the lever, it defaults to addition.
Comments
Screenshot
Didn't upload the image correctly, so use this. https://imgur.com/a/ftOiTpD