Sundial and fitness tracker: what they have in common

1. Step 1. Sundial — works like — Water clock (clepsydra). Two ancient ways to measure time: by a shadow and by flowing water.
2. Step 2. Water clock (clepsydra) — evolved into — Mechanical clock. Mechanical clocks replaced water clocks, swapping the flow of water for an escapement.
3. Step 3. Mechanical clock — includes — Wristwatch. A wristwatch is a mechanical clock made small enough to wear.
4. Step 4. Wristwatch — evolved into — Smartwatch. The form factor of a wristwatch.
5. Step 5. Smartwatch — evolved from — Fitness tracker. Tracker functions moved into watches.

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