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

1. Step 1. Cistern — is made of — Stone. Cisterns were cut into rock or lined with stone.
2. Step 2. Stone — is material for — Interferometer. Michelson’s instrument stood on a stone slab.
3. Step 3. Interferometer — inspired — Theory of relativity. The Michelson–Morley experiment found no ether.
4. Step 4. Theory of relativity — is used in — GPS (satellite navigation). Corrections for the relativistic slowing of clocks.

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