Score
0
Round
1/10
Best
-
An eyeballing test. Mark the midpoint of a line, the centre of a circle, a right angle, an angle's bisector, the missing corner of a parallelogram and the centre of a triangle — by eye alone. Ten rounds, up to 100 points each.
Each round shows a shape and a short instruction above it. Six kinds of task come up: the midpoint of a line, the centre of a circle, the direction that makes a right angle with a given arm, the line that splits an angle in half, the fourth corner that completes a parallelogram, and the centre of a triangle (its centroid, where the three medians meet).
Press on the board and slide to aim. On a touch screen the crosshair floats a little above your fingertip so your finger never hides the spot. For the two angle tasks a dashed arm follows your aim from the corner. Lift your finger to lock the point in.
The correct answer then appears in green. Your score for the round depends only on how far off you were, relative to the size of the shape: a perfect mark earns 100, and you get nothing once you miss by 12% of the shape's size — or by 12 degrees on the angle tasks. After ten rounds your total is your score.
Use symmetry instead of measuring. For a midpoint, imagine folding the line so the two ends meet; for a circle's centre, look for the point where the horizontal and vertical widths are both split evenly. Your eye is much better at judging whether two halves look equal than at estimating a distance directly, so let it compare rather than count.
Right angles are easiest when you think in terms of the grid your screen already gives you. A rotated arm is hard to judge on its own, but if you picture a small square leaning against it, the perpendicular side of that square is exactly where you want to aim. For bisectors, trace each arm outward in your mind: the bisector points to the spot that is equally far from both.
The parallelogram's missing corner is found by copying a move: whatever step takes you from the middle corner to one end, repeat it from the other end. For the triangle's centre, it helps to know the centroid sits two-thirds of the way from any corner toward the middle of the opposite side — lower than most people guess when the triangle points up.
Studies of 'eyeballing' show that most people have a consistent bias, such as placing midpoints slightly to the left (a well-documented effect called pseudoneglect) or missing right angles in the same direction every time. After a few runs, check the green answers against your marks. If you keep missing in the same direction, nudge your aim the other way on purpose; correcting a known bias is the fastest way to add points.