Pinhole and modem: what they have in common

1. Step 1. Pinhole — is part of — Camera obscura. It projects an inverted image.
2. Step 2. Camera obscura — evolved into — Camera. A camera is a camera obscura with a light-sensitive layer.
3. Step 3. Camera — has part — Exposure meter. A built-in light meter.
4. Step 4. Exposure meter — has part — Photodiode. A photocell.
5. Step 5. Photodiode — is used in — Fax. Scanning with a photocell.
6. Step 6. Fax — has part — Modem. It transmits an image over a telephone line.

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