Can You Match the Length?

Can you match the length of a line by drawing one of the same length at a different angle? A reference line is shown, then you draw a line elsewhere on the canvas. Only length matters. Angle is irrelevant. Your score is the percentage difference between your line's length and the reference. It sounds simple until you realize that orientation dramatically biases your perception of length.

How to Play

1. A reference line appears at a random angle on the canvas.
2. Draw your own line anywhere. Try to make it the same length.
3. The game measures your line's length and compares it to the reference.
4. Your score is the percentage error from the reference length.

Why It's Hard

The horizontal-vertical illusion causes vertical lines to appear about 20% longer than equal-length horizontal lines. When the reference and your drawn line are at different angles, you're fighting this perceptual bias. Drawing a horizontal match to a vertical reference will consistently produce a line that's too long; the reverse yields one that's too short.

Tips

• If the reference is vertical, draw your match slightly shorter than it looks. Your eye will overestimate vertical length.
• If both are diagonal, angle them similarly to minimize the orientation bias.
• Use canvas edges as a common ruler: note where the reference line's endpoints fall relative to the borders.

FAQ

Is this the same bias as in which-is-longer?

Yes, both games exploit the horizontal-vertical length illusion. Here you reproduce a length rather than compare two; the same perceptual bias applies but in a production task.

What error is top-tier?

Under 5% is excellent. Under 10% is solid. The orientation bias can cause 15–20% systematic error if not corrected for.

Does line thickness matter?

Slightly. Thicker lines appear shorter than thin lines of the same length. The game keeps line thickness uniform across reference and drawn lines.