French Curve

French curve is designed to create curves that cannot be constructed with a compass.   To use a French curve, plot points that are known to lie on the curve and fit the instrument to the points.

French curves are useful for making curves whose radius changes.

French curves are available in a wide variety of shapes and sizes.  They typically only fit a short section of the curve.

French curves are available in a wide variety of shapes and sizes.

Flexible rules are available for the same purpose, but they do not produce as good results as French curves.