Make a shadow stick. Push a pencil upright into a ball of clay on a sheet of paper in the sun. Mark the tip of its shadow every half hour with a dot and the time. When is the shadow shortest? That is local noon.

Before chapter 3. Beto writes "a clock" first. Why does Ledger stop him?

The answer. Because the slip is for what is there, before what you think it is. Looking first is how Lan noticed the lines. In the book, Eratosthenes found that the noon shadow in Alexandria made 7.2 degrees, which is a fiftieth of a full turn (360 ÷ 7.2 = 50). The distance to Syene was 5000 stadia, so the Earth was about 50 × 5000 = 250,000 stadia round.

The honest part. Nobody knows exactly how long Eratosthenes' stadion was, so we cannot say how close he got.

The grown-up layer. Writing "what I see" before "what I think" is the habit of a field scientist. FieldForge practises it, and MeasureQuest has Bevel (angles) and Rod (lengths).

For the ride home. Ask: what is too big to measure with a ruler?