Clock dial and atomic clock: what they have in common

1. Step 1. Clock dial — is part of — Tower clock. Large dials on the faces of the tower.
2. Step 2. Tower clock — is a kind of — Mechanical clock. A clock.
3. Step 3. Mechanical clock — evolved into — Quartz clock. Quartz clocks replaced mechanical ones: a vibrating quartz crystal took the place of the pendulum and balance.
4. Step 4. Quartz clock — evolved into — Atomic clock. The quartz oscillator is tuned to an atomic standard.

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