Monthly calendar pages and atomic clock: what they have in common

1. Step 1. Monthly calendar pages — is part of — Wall calendar. A grid of days.
2. Step 2. Wall calendar — uses — Gutenberg printing press. Printing.
3. Step 3. Gutenberg printing press — is used in — Mercator projection. Maps were printed in large numbers.
4. Step 4. Mercator projection — is a kind of — Map. A projection.
5. Step 5. Map — evolved into — GPS (satellite navigation). Digital navigation on a map.
6. Step 6. GPS (satellite navigation) — uses — Atomic clock. The satellites carry atomic clocks; the position is calculated from signal arrival times.

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