The story in three lines. Lan and Inkling arrive in a brick street in Mohenjo-daro, where two teams are building a covered drain from opposite ends to meet tomorrow. Measuring in hands fails because the builders' hands differ, and each team's own stick fails because the two sticks differ. Inkling asks whether both teams could use one length, and Lan asks the boy to copy his team's stick exactly and run the copy to the other team. The two halves meet even.

One question to ask. "Why did the two sticks not work, when each team measured carefully?" Then: "Why is every ruler in the shop the same length?"

One thing to do at the table. Measure the table with your hand spans, and ask someone else to do the same; compare the numbers. Then measure it again with two rulers, or one ruler and a tape measure, and see that they agree.

The grown-up layer. The idea is a standard unit: one shared length, copied for everyone, lets people who work apart make things that fit. Indus builders made bricks in the same proportions in many cities, and used standard weights and finely marked rulers. The Honest Page says their writing is unread, so nobody knows how they agreed their measures. This time Lan says the answer too soon and it buzzes. With this book the third word is complete: WIDE. The anvil now reads DOOR OPEN WIDE.