A system designed to draw straight lines and perfect circles freehand - video embedded below:
This table helps you to draw precise freehand circles and lines. It is under development by a group in the Yasuaki Kakehi Lab at Keio University.
By using a computer to control the XY position of a magnet under the surface of the table, it implements, on paper, drawing methods utilized in computer graphics.
"I’ll place an ordinary ballpoint pen on the table. Now, I can semi-automatically draw a precise circle, or a straight line, or an illustration prepared in advance. In other words, while I draw with the pen, this system lets me switch to accurate rendering like in computer graphics, such as drawing a precise circle, by assisting me with the pen."
When drawing, you can use a regular ballpoint pen with a metal tip, or a digital pen. If you use a ballpoint pen, the position where you start drawing has to correspond with the origin on the XY grid, but if you use a digital pen, the system recognizes its location and you can start drawing from any position.