Snappy Viper GAIN autonudge bug

Here is a door-open recreation of a bug in the autonudge code in Snappy Viper. I was delighted to see that what caused me the greatest problem in simulating this also caused headaches for the professionals.
Having said that, I noticed nothing as a kid and it’s taken me eight months to spot an error! Hats off to those who put these together in the 1980s!