Ow, this - when you're thinking "need to do this" while coding and you're *so sure* you did it but in fact you didn't - totally did that yesterday in the work for my PhD. Spent the whole day trying to find a bug in an algorithm, only to find out that it was in fact perfectly correct, I had just accidentally mixed up the top and bottom coordinate while drawing the result. And I clearly remember thinking "no, in this case I get the bottom, need to subtract height first!" when I was writing it, but when I finally looked at it again, there was only glaring whitespace...