Questions About Figure Placement

[dethinate]

Page 34 of Figure Drawing for All Its Worth shows how to place figures in a scene. I dont understand the last panel "Here are two levels". It seems simple but it's utterly confusing. Can anyone give me some help?

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There are two levels: the ground plane and the top of the steps. To relate the figures on the ground plane to the figure on the steps, he is dropping the measuring line, which measures the length of the figure on the steps, down onto the ground plane, and uses it to construct the length of the figures on the ground. It is what he is doing in the preceding diagrams, with that extra 'droppping' step...