It’s personal PIN numbers. First two digits on the x-axis, last two on the y-axis. Black/red = few, Yellow/white = many. Note the diagonal and the vertical line indicating birth years. https://t.co/HKYKWVhBiY

It’s personal PIN numbers. First two digits on the x-axis, last two on the y-axis. Black/red = few, Yellow/white = many. Note the diagonal and the vertical line indicating birth years. https://t.co/HKYKWVhBiY