Scythe snath and programmable logic controller: what they have in common

1. Step 1. Scythe snath — is part of — Scythe. A long handle.
2. Step 2. Scythe — is made of — Iron. Scythes appeared with 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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