Called the "Constrained Ball", this attachment can be easily attached on any pen and can help you draw straight lines, horizontally or vertically.
It's a small attachment with a very simple design and an attractive look.
The constrained ball lets you draw straight lines vertically, horizontally and even diagonally with one sweeping motion with any pen. It can also be used to measure a length of line which is clearly indicated on the tip.
Because of its adjustable rubber lining, any size of pen can easily be attached to this.
Seen above, the constrained ball product easily follows the line on the graph and indicates the length of the line already drawn.
You can use it to underline your notes neatly.
The constrained ball, a very useful product design that can be used by architects, designers, students, and just about anyone who needs to draw a straight line.
Who needs a ruler with a pen attachment like this. It draws and it measures!