Holt tracked tractor and programmable logic controller: what they have in common

1. Step 1. Holt tracked tractor — evolved into — Bulldozer. A bulldozer is a tracked tractor with a blade.
2. Step 2. Bulldozer — has part — Hydraulic cylinder. The blade is raised by hydraulics.
3. Step 3. Hydraulic cylinder — has part — Piston. The piston is moved by liquid.
4. Step 4. Piston — is part of — Insulin pump. The reservoir’s plunger.
5. Step 5. Insulin pump — has part — Microprocessor. A dosing controller.
6. Step 6. Microprocessor — is part of — Programmable logic controller. A processor.

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