A rule is a basic straight edge for drawing straight lines or if a French curve, for drawing curved lines. Square sets allow a predetermined angle to be drawn. Scales are rules with a graduated scale along the edge so a line of predetermined length can be drawn or a line distance measured. Parallel rules are composed of two separate rules with pivoting hinges for drawing parallel lines, and rolling rules have cylindrical rollers inserted through them so the rule can be rolled to maintain parallel lines.