How does the straight line test work?
There is no Start button: the box is the test. Press, draw one line across it in any direction, and let go. Your score appears straight away, with the best-fitting true line drawn dashed over yours, so you can see where yours bent. Draw again as often as you like; your straightest line of the visit is kept. Lines shorter than 160 pixels, and lines that go back over themselves, aren't scored.
How is your result calculated?
Your line is spaced out into evenly placed points, and the straight line that fits them best is found. The distance of each point from that line is measured, and their root-mean-square, as a share of the line's length, is your line's wobble. Straightness is 100% at no wobble and falls along a curve to 0% at a wobble of 5% of the length. Because everything is relative to your line's own length, screen size doesn't matter.
What do different lines score?
These are computed by the same code that scores your line. A gentle bow, bending 3% of its length at the middle, scores 91%. A wavy line that wobbles 3% either side scores 74%. A strong bow, bending 10% of its length, scores 50%. Only a line that is exactly straight scores 100%.
Why is it hard to draw a straight line?
Your hand moves on joints that turn, so a movement from the wrist or the elbow naturally traces an arc. Drawing straight means combining several joints at once so their arcs cancel out, all while watching the line. Short lines are easier because one joint can almost manage them alone.
- Move from the shoulder. A whole-arm movement curves less than a flick of the wrist.
- Look at where you are going. Fix your eyes on the end point, not on the tip of the line.
- Keep a steady speed. Slowing down or speeding up mid-line is where wobbles appear.
For the round version, try Draw a Perfect Circle; to follow an outline instead of drawing freehand, the Shape Tracing Game.