Inside a circle divided into 10 segments—representing the numbers zero to nine—each digit of pi links to the the next with a line. Krzywinski added an outer layer to Vasile’s illustration. He measures how frequently one digit follows another. For example, in a sequence like 2739452781, the transition 2 to 7 occurs twice. Krzywinski uses bubbles to represent these transitions: the larger the dot, the more times a sequence occurs.