Eyeball It

How to play

Eyeball It is a geometry precision game in 10 rounds. Each round shows a fresh figure and asks for one exact spot: the midpoint of a segment, the center of a circle, the corner that makes a right angle, the line that splits an angle in half, the missing corner of a parallelogram, the centroid or incenter of a triangle, the point where three lines would meet, or the foot of a perpendicular. Drag the orange marker to where you think the spot is, then confirm. No rulers, no grid — just your eye. The true answer appears in green with the construction behind it, along with your error in pixels. Errors are measured on a fixed 500 × 500 reference board, so a pixel means the same thing on a phone and on a big monitor. After 10 rounds you get your average error; the lower, the better. Every game brings new random figures, so you can play as many games as you like and climb the leaderboard.

Tips

• Look at the whole figure before you move: your first instinct is often better than staring at one spot.
• For midpoints and centers, compare both sides at once instead of measuring one side at a time.
• Right angles: imagine the corner of a sheet of paper laid on the line.
• Centroid and incenter are different points — the centroid leans towards the bulk of the triangle, the incenter sits equally far from all three sides.
• On desktop, finish with the arrow keys: one tap moves the marker by a single pixel.
• Every game has new figures, so play a few in a row: once your eye warms up, your average error usually drops.