Graduated wooden staff and optical telegraph: what they have in common

1. Step 1. Graduated wooden staff — is part of — Jacob’s staff. A long bar with a scale.
2. Step 2. Jacob’s staff — evolved into — Davis quadrant. Davis spared the navigator from looking at the Sun.
3. Step 3. Davis quadrant — evolved into — Octant. Reflecting angle gauges.
4. Step 4. Octant — evolved into — Sextant. The sextant is an extended octant.
5. Step 5. Sextant — has part — Lens. The sextant’s telescope.
6. Step 6. Lens — is used in — Optical telegraph. Signals were read through telescopes.

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