Abstract: A transparent ruler with a U-shaped slot, a multiplicity of separate scales, and reference numbers. The scales are exactly perpendicular to each other, with one being horizontal and the others being vertical. Three slots are on the ruler, two of which are parallel with the vertical scales and one of which is parallel to the horizontal scale. The slots intersect so as to form one big square U-shaped slot. There are arrows on the top and side edges of the ruler which are collinear with the slots. These arrows are used for reference purposes when extending a line, squaring a line with respect to another line, etc. The vertical scales are used to draw perfectly parallel lines with respect to the horizontal slot.