Sundial gnomon and GPS (satellite navigation): what they have in common

1. Step 1. Sundial gnomon — is part of — Sundial. A rod that casts a shadow.
2. Step 2. Sundial — works like — Water clock (clepsydra). Two ancient ways to measure time: by a shadow and by flowing water.
3. Step 3. Water clock (clepsydra) — evolved into — Mechanical clock. Mechanical clocks replaced water clocks, swapping the flow of water for an escapement.
4. Step 4. Mechanical clock — evolved into — Quartz clock. Quartz clocks replaced mechanical ones: a vibrating quartz crystal took the place of the pendulum and balance.
5. Step 5. Quartz clock — evolved into — Atomic clock. The quartz oscillator is tuned to an atomic standard.
6. Step 6. Atomic clock — is used in — GPS (satellite navigation). The satellites carry atomic clocks; the position is calculated from signal arrival times.

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