Crutch underarm pad and micrometer: what they have in common

1. Step 1. Crutch underarm pad — is part of — Crutches. A padded crossbar.
2. Step 2. Crutches — uses — Lever. A support.
3. Step 3. Lever — is used in — Vernier caliper. The jaws open like a lever.
4. Step 4. Vernier caliper — evolved into — Micrometer. A more precise instrument.

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