Machine features two 4-Bit Inputs, A and B, 3 Function selectors, for A+B, A-B, and A*B, and also 8 bit lamp output. The adder/subtractor is an ICA adder with XORs o nthe B inputs for 2-s complement subtraction. The multiplier is a combinational 4-Bit multiplier using the same adder design, and shifting for combinational. The adder/Subtractor outputs do NOT use the adders C Out, so only a 4 bit output. An overflow in the adder will only return the 4 lsbs.
For your inputs, there are 2 rows of 4 levers. The inputs are 4 bit binary numbers, A on top and B on bottom. Least Significant Bit is on the right for both input and output. To the right of the inputs are three levers, the left is add, middle is subtract, and right lever is multiply. Flip the lever for whichever function you want. Then, to the left of the binary inputs, are 8 lamp columns for a binary output. The back wall has signs about some basic things and start/finish dates. The subtractor does support negative numbers, but the output is in two's complement (ie. 0011-0101, or 3-5, outputs 1110, or 14. 1110 is also the two's complement of -2, because inverted+1 0010 is 1110).