Sliding transom and plough: what they have in common

1. Step 1. Sliding transom — is part of — Jacob’s staff. A movable arm for measuring the angle.
2. Step 2. Jacob’s staff — works like — Quadrant. Two angle gauges for measuring the altitude of celestial bodies.
3. Step 3. Quadrant — has part — Plumb bob. A plumb line shows the vertical.
4. Step 4. Plumb bob — is made of — Stone. The bob of a plumb line is stone or copper.
5. Step 5. Stone — is material for — Hoe. The working part was of stone or antler.
6. Step 6. Hoe — evolved into — Plough. The plough mechanized loosening the soil with a hoe.

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