I’ve seen this before but have just been reminded of it again in a post by Mr H at Sargent Park Math Zone

The eyeballing game

The Eyeballing Game is an interactive visual estimation game. In the Eyeballing Game players are presented with a drawing or a line segment, angle, or shape. Players are then given a task like “find the spot equidistant to all sides” or “bisect the angle.” From Mr Bryne at Free Technology for Teachers