The last section in chapter 3 about aggregates mentions “„Aggregates perform some kind of calculation on records in a relationship“. However, when unterstand this change right, it might no longer be restricted to relationships but can be pointed directly at resources too:

I think this should at least be mentioned as it was part of the v3.5.35 release.

Also as aggregates completely replace the before constructed calculations one wonders what calculations are then for when they can be easier done with aggregates. The book should make a comment about this.