Coin obverse and reverse faces and atomic clock: what they have in common

1. Step 1. Coin obverse and reverse faces — is part of — Coin. Front and back with pictures.
2. Step 2. Coin — is made of — Gold. The first Lydian coins were made of electrum, an alloy of gold and silver.
3. Step 3. Gold — is material for — Wristwatch. The case is gold or silver.
4. Step 4. Wristwatch — is a kind of — Mechanical clock. A wristwatch is a mechanical clock made small enough to wear.
5. Step 5. Mechanical clock — evolved into — Quartz clock. Quartz clocks replaced mechanical ones: a vibrating quartz crystal took the place of the pendulum and balance.
6. Step 6. Quartz clock — evolved into — Atomic clock. The quartz oscillator is tuned to an atomic standard.

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