Hypocaust and micrometer: what they have in common

1. Step 1. Hypocaust — is made of — Brick. The pillars of a hypocaust are brick.
2. Step 2. Brick — is made of — Clay. Bricks are moulded from clay.
3. Step 3. Clay — is material for — Movable type. Bi Sheng’s type was made of fired clay.
4. Step 4. Movable type — works like — Interchangeable parts. Movable type is an early case of interchangeable parts: identical letters move from line to line.
5. Step 5. Interchangeable parts — uses — Micrometer. Precise measurement ensures interchangeability.

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