Practicing without playing

Homework!!!  I am to old for homework. But since I don't have time today to actually practice my guitar I guess I will have to do some other practice work. Namely scales. Not on the guitar, but on paper. I have to say that those people who put that whole modern musical scale together were genius. The circle of fourths (and fifths) is amazing. Major scales get one more sharp as you go around one way and one more flat as you go the other.