I remember in Polish computer magazines, they had a validation program. It was a shorter program that you typed in once and ran. Then, when typing in the long "

I remember in Polish computer magazines, they had a validation program. It was a shorter program that you typed in once and ran. Then, when typing in the long "game" code from the magazine, the screen displayed two-letter checksums for each line of codde. The two-letter checksum was also put in the code listing in the magazine, so that you could quickly compare them to find the line that was typed wrong.