Ellipse compasses

Before you just could drag your mouse to get an ellipsis of any size both templates and special mechanical devices were used. The two devices depicted use different methods of drawing an ellipse.
The method using a thread is at least still used by gardeners. Using a sharp pencil, thin pins and a thin thread you can get quite a good precision by this method first described at least by Descartes (1596 - 1650):
Based on the desired long and short axes you can construct the positions of the focal points where the pins are inserted
f = sqrt (a2 - b2)
The length of the thread is
2(a+ f)