Signal post and gyroscope: what they have in common

1. Step 1. Signal post — is part of — Railway semaphore. A post.
2. Step 2. Railway semaphore — evolved from — Optical telegraph. The semaphore idea.
3. Step 3. Optical telegraph — uses — Telescope. Signals were read through a telescope.
4. Step 4. Telescope — includes — Space telescope. A space telescope is a telescope above the atmosphere, so air does not blur the view.
5. Step 5. Space telescope — has part — Gyroscope. Pointing gyroscopes.

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