Draw a Perfect Circle

• Roundness: 100% minus how far your line strayed from the best-fitting circle, on average, as a share of that circle's radius. A line that wobbles by 2% on average scores 98%.
• The colors of your line: green where the line sits on the circle, through yellow, to red where it strays far.
• The dashed circle: the best-fitting circle for your drawing. The closer your line hugs it, the higher the score.
• Your best: your highest score in this browser, kept separately for touch and for mouse, because a finger and a mouse draw very differently.
• Direction: clockwise or counterclockwise. Most people in the US draw counterclockwise; in Japan most draw clockwise [1].

1. Draw. Put your finger (or the mouse button) down anywhere and draw one circle around the dot, in one stroke.
2. Watch it live. Once you have gone part of the way round, the roundness shows in the middle and the line changes color.
3. Lift. When you finish, the best-fitting circle appears dashed and your drawing is scored.

To count, a drawing must go at least 320° of the way round, end close to where it started, be big enough (a radius of at least 15% of the drawing area's width) and take less than 30 seconds. Just one loop, please. Every finished drawing is scored on our server with the same formula: we fit a circle to your points by least squares and measure the average distance of the points from it. Results are saved with the kind of input you used, so finger circles are compared only with finger circles, as our privacy policy explains.

Drawing a circle asks your shoulder, elbow, wrist and fingers to work together while the direction of the movement changes all the time. Your hand naturally speeds up and slows down with the curve [2], and every change of speed is a chance to drift outward or inward. On a phone, your finger also hides the line you are drawing. A mouse moves the whole arm, which is why mouse circles and finger circles score differently.

• Draw bigger and with the whole arm. Small circles from the fingers alone wobble more.
• Keep an even speed. Not too slow: very slow drawing tends to shake.
• Look at the center dot, not the line. Keeping the same distance from the center is the whole task.
• Close the loop smoothly. Many circles lose points at the end, where people rush to meet the start.

The circle test is a fun hand-control challenge. Your score depends on your device, your screen size, whether you use a finger, pen or mouse, and on practice. It is not a medical test or a tremor test; doctors use other drawing tasks, such as spirals, for that [8]. Drawing direction says nothing about your health.