1. Although this rule give the appearance of having been made "down to a price" it has a very good complement of scales.
2. Indeed, given the need to keep some scales (A and B for example) adjacent to each other on stock and slide, it could be considered close to optimum. For example, on once face the LL02 and LL03 on the top are balanced by the LL2 and LL3 on the bottom, whilst on the other face the LL01 if balanced by the LL1.