Sharp stone edge and GPS (satellite navigation): what they have in common

1. Step 1. Sharp stone edge — is part of — Hand axe. A sharp edge around the perimeter.
2. Step 2. Hand axe — evolved into — Axe. A hand axe mounted on a handle.
3. Step 3. Axe — is made of — Stone. A Neolithic axe is ground stone on a handle.
4. Step 4. Stone — is material for — Interferometer. Michelson’s instrument stood on a stone slab.
5. Step 5. Interferometer — inspired — Theory of relativity. The Michelson–Morley experiment found no ether.
6. Step 6. Theory of relativity — is used in — GPS (satellite navigation). Corrections for the relativistic slowing of clocks.

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