Second, they write with the greatest ink flow when perpendicular to the paper, but as the angle is increased the line width gradually decreases; at some angle, when the edge of the ball socket brushes against the surface of the paper, the line width is reduced to zero and the pen ceases to write. By contrast, a rollerball pen has a thin line when perpendicular to the paper, but the line width increases suddenly as the angle is increased and a blob forms between the tip of the ball and the edge of the socket.