As others have mentioned, the publishers had developed and distributed a checksum tool, written in BASIC, that you could type in from scratch as well. Although

As others have mentioned, the publishers had developed and distributed a checksum tool, written in BASIC, that you could type in from scratch as well. Although I think I copied mine from a friend who did subscribe to the monthly diskette version. So you couldn't enter a line wrong, it would get flagged right away. As far as debugging the whole thing, I think they just published a dump of the known-good copy they received with the user's submission. I think you had to provide two separate, working copies of your program along with the source code?