A zigzag of straight edges. The rough bolt appears within a few circles; the last ones sharpen the corners. With few circles, look for the small overshoot at each corner: the Gibbs phenomenon.
Measuring the shape…
Each path of the lightning bolt is traced by a chain of circles, each one spinning on the tip of the one before. A Fourier transform measures the path and works out every circle's size, speed and starting angle. The circles are sorted biggest first, so the first few give the rough shape and the rest add detail.
"Within 1%" means the drawing is, on average, less than 1% of its width away from the real outline. The bars show the circles of the main outline: height is size, position is how many times it turns per loop and in which direction. Click a bar to remove that circle and see what it was doing. Learn how it works.