Paper screen with grease spot and aeroplane: what they have in common

1. Step 1. Paper screen with grease spot — is part of — Photometer. The spot vanishes when both sides are equally lit.
2. Step 2. Photometer — uses — Reflection of light. Brightness is judged from reflected light.
3. Step 3. Reflection of light — is used in — Stealth technology. Facets reflect waves off to the side.
4. Step 4. Stealth technology — is used in — Jet fighter. Low observability.
5. Step 5. Jet fighter — is a kind of — Aeroplane. An aircraft.

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