System 1 audit and test numbers
0 coins chute 1; 1 coins chute 2; 2 total plays; 3 replays; 4 slam tilts; 5 extra balls; 6 tilts; 7-9 first, second and third replay levels; 10 high score to date. Test 11 counts players 1 and 3 displays from 000000 to 999999, 12 does players 2 and 4 (the credit display is not tested), and 13 is the lamp, coil and switch test.
Systems
Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)