Theodolite and tunnelling shield: what they have in common

1. Step 1. Theodolite — has part — Lens. A telescope.
2. Step 2. Lens — is part of — Otoscope. A lens.
3. Step 3. Otoscope — has part — LED. Illumination.
4. Step 4. LED — is part of — Street light. LEDs.
5. Step 5. Street light — is part of — Tunnel. Lighting.
6. Step 6. Tunnel — uses — Tunnelling shield. Shield tunnelling.

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