Oh HEY, this is probably related to both how I can re-balance scheduling books on the fly and to how I do time management professionally. That actually makes a lot more sense, now.

(I don't actually do arithmetic for either, particularly the professional time management, because it's *incredibly* stressful for me to try to to deal with numbers. Instead I do visual and/or mental representations of various discrete chunks of stuff and manipulate *those*. But that sort of visualisation is, I have gathered, not a universal thing at all! Which is why I was bemused even though I could see the potential utility for other people of putting it into a more familiar context.)