Ruler body and railway track: what they have in common

1. Step 1. Ruler body — is part of — Ruler. Wood, metal or plastic.
2. Step 2. Ruler — evolved into — Vernier caliper. Precise measurement of dimensions.
3. Step 3. Vernier caliper — uses — Lever. The jaws open like a lever.
4. Step 4. Lever — is used in — Railway switch. Switched by a lever or a motor.
5. Step 5. Railway switch — is part of — Railway track. Switches.

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