What is a perfect cross in geometry?

A perfect cross (or orthogonal bisection) consists of two line segments that intersect at right angles (90°), have equal length, and bisect each other — meaning each line's midpoint is the intersection point. This is the geometry of a plus sign (+) or a Christian cross with equal arms.

How is the cross quality score weighted?

Perpendicularity error is weighted 1.5×, midpoint coincidence 1.2×, and length mismatch 0.8×. In practice, getting the 90° angle right has the biggest impact on your score. A 10° angle error will cost more than a 10% length mismatch.

Why is a click-based game harder than a freehand draw?

With freehand drawing, you get continuous visual feedback as you draw and can self-correct mid-stroke. With discrete clicks, each point is committed immediately — there's no undo. This forces deliberate spatial planning before each click rather than real-time motor correction.

Can You Draw a Perfect Cross?

Drawing a perfect cross — two perpendicular lines of equal length that bisect each other exactly at their midpoints — sounds like the simplest geometry challenge on the site, but the scoring is unforgiving on three simultaneous constraints. This game uses a click-based rather than freehand approach: you place four points (two endpoints per line), and the algorithm checks perpendicularity, length equality, and midpoint coincidence all at once. Getting all three right simultaneously is harder than it sounds.

How to Play

Press Start. A HUD prompt tells you which point to click next.
Click two endpoints for the first line, then two endpoints for the second line (4 clicks total).
The two lines should be perpendicular (90° apart), the same length, and cross at their exact midpoints.
Press Submit after placing all four points. The score is a weighted composite of perpendicularity error, length mismatch, and midpoint offset.
There is no dragging — each click is final. Plan your four points before you start clicking.

Why It's Hard

Perpendicularity requires estimating a 90° angle relative to an arbitrary line you just drew — which is harder when that line isn't axis-aligned. Length matching without a ruler forces you to rely on visual estimation, which is subject to the Müller-Lyer illusion (lines pointing in different directions look different lengths even when identical). And midpoint coincidence requires that both midpoints land on the same pixel, which compounds errors from both the length and perpendicularity judgements.

Tips

1Draw the first line at a 45° diagonal — perpendicularity to a 45° line is easier to judge by eye than perpendicularity to a near-horizontal or near-vertical line.
2After placing your first two points, estimate the midpoint visually, then place the second line's points equidistant from that midpoint.
3Use the grid in the background as a ruler — align your clicks to grid intersections to get clean 90° angles.

FAQ

What is a perfect cross in geometry?: A perfect cross (or orthogonal bisection) consists of two line segments that intersect at right angles (90°), have equal length, and bisect each other — meaning each line's midpoint is the intersection point. This is the geometry of a plus sign (+) or a Christian cross with equal arms.
How is the cross quality score weighted?: Perpendicularity error is weighted 1.5×, midpoint coincidence 1.2×, and length mismatch 0.8×. In practice, getting the 90° angle right has the biggest impact on your score. A 10° angle error will cost more than a 10% length mismatch.
Why is a click-based game harder than a freehand draw?: With freehand drawing, you get continuous visual feedback as you draw and can self-correct mid-stroke. With discrete clicks, each point is committed immediately — there's no undo. This forces deliberate spatial planning before each click rather than real-time motor correction.

Built by

Ethan R. Caldwell

Game Developer · Wilmington, DE

Designed Can You Draw a Perfect Cross? and 46 other browser puzzles. Game developer based in Wilmington, Delaware. Hardcore puzzle gamer at heart — obsessed with logic puzzles, sokoban-style mechanics, and physics-based brain teasers. Off the clock, unwinds with ARPGs, RPGs and JRPGs.

[email protected]