Yeah, this was pointed out to me after publishing. Specifically, when the ASM was converted over /specs, it incorrectly wrote the amount of sales tax to the specs. Thus, the z80 implementation took that incorrect /spec and made it happen. At this stage, I'm sure if I had put some more care/effort into transpiling something from the source (i.e., connecting two or more LLMs as a check on that process) to specs, this problem could have been avoided.