The Constrained Ball is a drawing device created by Korean product designer Giha Woo.
This device is meant to help people draw straight line without using a ruler by applying a controlling wheel to the ball-pen that makes it roll in only one direction.
It also comes with a measurement gadget, that tells you in every moment how long is the line you have drawn, so you can draw it to the exact length you wish.
The mounting area is made with a flexible rubber material to provide the best tightness. In addition to horizontal and vertical lines you can also easily draw 45 angled lines.
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