Switch form codes: A, B and C

A contacts entry such as 4A,1B,2C means four normally open (form A) switches, one normally closed (form B) and two make/break (form C) on that relay.

Systems

• Electro-mechanical

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)