Balance beam and telescope: what they have in common

1. Step 1. Balance beam — is part of — Shaduf. A long pole acting as a lever.
2. Step 2. Shaduf — uses — Lever. A shaduf is a lever with a counterweight.
3. Step 3. Lever — is used in — Optical telegraph. The arms were moved by a system of levers and rods.
4. Step 4. Optical telegraph — uses — Telescope. Signals were read through a telescope.

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