What is the difference between the straight line test and the horizontal line test?

The straight line test (another game on this site) measures deviation from an arbitrary diagonal line between two fixed points — it tests raw linearity. The perfect horizontal line test specifically measures levelness: whether your line stays at a constant height. A line can be perfectly straight diagonally but fail the horizontal test badly if it is tilted.

How is the levelness score calculated?

Two metrics are combined: slope (the Y difference between where your line starts and ends) and wobble (the maximum deviation from your line's mean Y value). Slope is weighted at 40% and wobble at 60%. Each metric maps 0 → 100 at 0 px deviation, dropping to 0 at around 80 px deviation. The final score is a weighted combination of both.

Can artists draw perfectly horizontal lines?

Professional illustrators and architects are measurably better than untrained adults, but nobody draws a perfect horizontal freehand without practice. Technical illustrators develop a wrist-locking technique and use long, rapid strokes to minimize tremor. Some traditional Chinese calligraphers practice horizontal strokes for months before attempting them in finished work.

Can You Draw a Perfectly Horizontal Line? — Line Test — Play Free

Can you draw a perfectly horizontal line freehand? It sounds trivial — until you try. The perfect horizontal line test challenges you to draw freehand across a blank canvas, then measures how level and straight your line actually is. Two metrics determine your score: wobble (how much your line deviates up and down) and slope (how much it tilts from start to finish). Most people discover that their "perfectly flat" line has a surprising amount of both. Three rounds, scored and averaged.

How to Play

Press Start. A blank canvas appears — draw a horizontal line from the left side to the right side using your mouse or finger.
Try to keep the line at a consistent height all the way across. Do not aim for a specific position, just focus on keeping it flat.
Release or lift your finger when you reach the right side, then press Submit.
The guide line (perfect horizontal at the midpoint) appears in blue. Your line is shown in red for comparison.
Your Levelness score combines wobble and slope penalties. After 3 rounds, scores are averaged.

Why It's Hard

Drawing a horizontal line freehand requires your hand to maintain constant Y-axis position while moving steadily in X. In practice, wrist joints naturally arc rather than slide, introducing a subtle curve. Muscle tremor (physiological tremor at 8–12 Hz) adds micro-oscillations. And without a physical ruler or guide, there is no tactile feedback confirming your position — you rely entirely on proprioception, which is less accurate than you think. The result is a line that feels flat but measures anything but.

Tips

1Draw from the elbow, not the wrist — sliding your whole forearm laterally produces a straighter path than rotating your wrist joint.
2Find a visual anchor point at your target height on the right edge of the canvas and keep your eyes fixed there as you draw toward it.
3Draw at medium speed: too slow gives tremor time to accumulate; too fast makes it hard to hold position.

FAQ

What is the difference between the straight line test and the horizontal line test?: The straight line test (another game on this site) measures deviation from an arbitrary diagonal line between two fixed points — it tests raw linearity. The perfect horizontal line test specifically measures levelness: whether your line stays at a constant height. A line can be perfectly straight diagonally but fail the horizontal test badly if it is tilted.
How is the levelness score calculated?: Two metrics are combined: slope (the Y difference between where your line starts and ends) and wobble (the maximum deviation from your line's mean Y value). Slope is weighted at 40% and wobble at 60%. Each metric maps 0 → 100 at 0 px deviation, dropping to 0 at around 80 px deviation. The final score is a weighted combination of both.
Can artists draw perfectly horizontal lines?: Professional illustrators and architects are measurably better than untrained adults, but nobody draws a perfect horizontal freehand without practice. Technical illustrators develop a wrist-locking technique and use long, rapid strokes to minimize tremor. Some traditional Chinese calligraphers practice horizontal strokes for months before attempting them in finished work.