Electrocardiograph and saw: what they have in common

1. Step 1. Electrocardiograph — evolved from — Galvanometer. Einthoven’s string galvanometer.
2. Step 2. Galvanometer — uses — Electromagnetism. The needle is deflected by the field of the current.
3. Step 3. Electromagnetism — is used in — Starter motor. A starter is an electric motor.
4. Step 4. Starter motor — evolved from — Crank. It replaced the starting crank.
5. Step 5. Crank — is part of — Sawmill. A crank turns the wheel’s rotation into the stroke of the saw.
6. Step 6. Sawmill — uses — Saw. The cutting tool is a saw.

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