Align

hang them straight. trust the bubble.

push crooked picture frames level with a spirit level, room by room, in as few nudges as you can

A spirit level's bubble rises to the high end of a curved glass vial and moves by the vial's radius times the tilt, so a finer vial shows a smaller tilt. That is why it beats your eye, which judges level by what surrounds a frame: a cornice in a settled house, or a picture engraved off true.

Concepts: order, precision.

An interactive you play with one thumb, on Wundr.