Fashcreat French curve with shoulder curve Ruler  (Set of 2, White)

French curves are used in drafting patterns or making pattern alterations. Invented in the late 1880s, the French curve is used by mathematicians, engineers and sewing a like. Technically a French curve is a drafting tool used to connect points in a smooth curve. It's used for garment pattern drafting and alterations, especially for necks and arms when trueing and blending seamlines.