I've been corrected (by somebody more alert) about bit numbers in PLC-5 I/O addressing; the bits are numbered 00 through 17, not 0 through 15.
PLC-2, PLC-3, and PLC-5 systems use Base 8 "Octal" addressing for I/O addressing. Only the digits 0,1,2,3,4,5,6,7 are used.
This can cause confusion because the PLC-5 uses Decimal addressing for Integer and Bit registers, and the SLC-500, MicroLogix, and ControlLogix use decimal addressing exclusively.
So always be careful when using Octal addressing to be sure that you are really looking at the correct bit; bit "10" is really the ninth point on the module.
It trips up even veteran programmers !