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Size Illusions Quiz

Ten questions at a time from a bank of 32. Each answer links to its source.

Useless’s lab notes: measured twice, rubbed out once

Jastrow said: “We judge relatively, even when we most desire to judge absolutely.” I judge relatively too. Next to a pencil sharpener, I’m enormous.

— U. (tap me for another)

Thanks for visiting. Trust your ruler, not your eyes.

The illusions

Müller-Lyer arrows
Ebbinghaus & Delboeuf circles
Ponzo & size constancy
The moon illusion
The Ames room
The T, Jastrow & sine
Experiments to try
Who found them

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The big facts page
Myths vs facts
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Useless’s lab notes

Helping

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The network

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About the network

size.illusions.im is part of the ReallyByte network, run by REALLYBYTE, based in the Isle of Man. Facts are checked against Michael Bach’s Optical Illusions & Visual Phenomena, Encyclopaedia Britannica and the Exploratorium, listed on the sources page (checked 31 Oct 2026). The illusion drawings and games are our own; photos are public domain or CC0, credited. Not affiliated with or endorsed by Michael Bach, Britannica or the Exploratorium. As an Amazon Associate I earn from qualifying purchases. No cookies; privacy-friendly visit counts via GoatCounter. Privacy | Contact

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