Semaphore tower and monitor: what they have in common

1. Step 1. Semaphore tower — is part of — Optical telegraph. A tower with movable sails.
2. Step 2. Optical telegraph — uses — Lens. Signals were read through telescopes.
3. Step 3. Lens — is part of — VR headset. Lenses.
4. Step 4. VR headset — has part — Display. A VR headset has two displays, one per eye.
5. Step 5. Display — is part of — Monitor. The heart of a monitor is the display: an LCD panel, once a picture tube.

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