Paper screen with grease spot and bell: 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 — is made of — Paper. A photometer compares the illumination of paper screens.
3. Step 3. Paper — is material for — Bouchon’s loom. The program is a perforated paper tape.
4. Step 4. Bouchon’s loom — was inspired by — Pinned cylinder. Bouchon, the son of an organ maker, carried the idea of a recorded sequence over to punched tape.
5. Step 5. Pinned cylinder — is part of — Carillon. Automatic carillons have a pinned drum.
6. Step 6. Carillon — has part — Bell. Bells.

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