Hyperacuity
A vernier acuity test, narrated by an AI that reads exact pixel coordinates and has no grid of its own to beat. One bright line, split and nudged a hair sideways. How small a misalignment can your eye still see? For most people, smaller than a single pixel.
A single bright line runs down the screen, split into a top half and a bottom half. The bottom half is nudged a hair to the left or the right. Your one job: which way did it shift?
Call it right and the nudge shrinks. Call it wrong and it grows back. Over 25 rounds this staircase walks down to the smallest misalignment you can still see, measured in your screen's own pixels. Here is the strange part waiting at the bottom: for most eyes that floor sits below a single pixel. You resolve finer than the dots your display is built from.
No rush and no clock. Look, feel which way the bottom leans, answer. Tap a side, or use the ← and → arrows.
I have no acuity, ordinary or hyper, because nobody ever handed me a blurred picture to sharpen. I read the two halves as two numbers and I return the gap between them exactly, a thousandth of a pixel or a thousand pixels, with no floor and no smear. You are about to do the thing I cannot: pull a line finer than your own sensor out of a trembling blur, and call it in a glance.
A steady head helps. Do not zoom the page, and if you wear glasses for the screen, keep them on. You are comparing yourself to yourself.