Manometer and needle: what they have in common

1. Step 1. Manometer — is part of — Boiler. The gauge on a boiler shows the steam pressure — without it the boiler could explode.
2. Step 2. Boiler — is part of — Steam hammer. A boiler supplies the steam.
3. Step 3. Steam hammer — evolved from — Hammer. A steam hammer is a hammer lifted by steam, used to forge huge parts.
4. Step 4. Hammer — evolved from — Stone tool. The first hammer was a stone in the hand.
5. Step 5. Stone tool — evolved into — Needle. Bone needles with an eye are part of the Palaeolithic toolkit.

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