Vernier scale and boiler: what they have in common

1. Step 1. Vernier scale — is part of — Vernier caliper. An extra scale for tenths.
2. Step 2. Vernier caliper — evolved from — Ruler. Precise measurement of dimensions.
3. Step 3. Ruler — has part — Measurement scale. Marked graduations.
4. Step 4. Measurement scale — is part of — Barometer. Millimetres of mercury.
5. Step 5. Barometer — works like — Manometer. Both measure pressure with a column of liquid: a barometer measures the air around us, a manometer the pressure inside a vessel.
6. Step 6. Manometer — is part of — Boiler. The gauge on a boiler shows the steam pressure — without it the boiler could explode.

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