Plier handles and programmable logic controller: what they have in common

1. Step 1. Plier handles — is part of — Blacksmith’s tongs. Long handles increase the force.
2. Step 2. Blacksmith’s tongs — is made of — Iron. Since the Iron Age, tongs have been made of iron.
3. Step 3. Iron — is material for — Relay. The armature and core are iron.
4. Step 4. Relay — evolved into — Programmable logic controller. It replaced relay cabinets.

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