Those equations look straight out of a book on how not to code layouts. If you need to tweak it to add an extra slot in the bottom right one day, you'll have to

Those equations look straight out of a book on how not to code layouts. If you need to tweak it to add an extra slot in the bottom right one day, you'll have to re-work on the entire set of equations. The constraints based method they talk about after is much better, though.