Polar Curve French Curves Small 320×80 Medium 640×160 Large 1024×256 Download TIFF Original 2400×599 | (77.0 KB) Description A Polar Spiral French curve, or irregular curve, is used to draw engineering diagrams and steam curves, and is plotted by using the polar equation. Keywords curve ruler, curve rulers, curved ruler, Polar Curve French Curves, Polar Curve Irregular Curve, polar curve ruler, polar equation, Ruler, rulers Galleries Mechanical Drawing Tools Source: French, Thomas E A Manual of Engineering Drawing for Students and Draftsmen (New York, NY: McGraw-Hill, 1911)