Ratio & Proportion in Pictures is the eighth book in the series, covering ratios in simplest form, ratios with units, the ratio of three numbers and ratios in the form 1 : n and n : 1. Map scales, and areas and gradients on maps. Dividing in a given ratio, and proportional sets of numbers. Applying ratio to similarity and enlargement and to areas and volumes of similar figures. Finally applying proportion to direct and inverse variation. 
There are galleries in the chapters covering similarity. Review questions are at the end of each section.
The review questions require iOS 10 or higher.