"On" == 0
SW18 is switch 18 as silk-screened onto the board.
- SW4[8] is the bit labled 8 on Switch 4.
+ SW4[8] is the bit labeled 8 on Switch 4.
SW2[1:6] refers to bits labeled 1 through 6 in order on switch 2
SW3[7:1] refers to bits labeled 7 through 1 in order on switch 3