You rest your finger from the other hand on the button in front, so when rolling the button is pressed. That way you can use more than one finger to press, whic

You rest your finger from the other hand on the button in front, so when rolling the button is pressed. That way you can use more than one finger to press, which allows faster pressing. The fastest rollers can hit the button around 20 times a second, whereas by holding the button down (i.e. manipulating DAS, the traditional technique) you can only reach 10 Hz.