A lot of machine code listings had per-line checksums which could be checked with a small auxiliary program. PC Magazine had assembly source for its free utilit

A lot of machine code listings had per-line checksums which could be checked with a small auxiliary program. PC Magazine had assembly source for its free utilities, alongside a BASIC program that would produce the utility from machine code encoded as hexadecimal numbers in DATA statements; the BASIC program also included checksums and would check the machine code as it ran.