Ruler and straightedge refer to tools or instruments that are used to measure the length or determine whether a surface is straight or to draw a straight line. A ruler is a tool used to measure the length, and a straight edge is a wooden or plastic instrument that is utilized for drawing straight lines. They are used in the automotive industries, and machining service. You can even use the side of a ruler, book, or piece of paper.
This tool is only used to make lines, not with which to measure. It is not the same as a ruler, which has the markings to be able to measure. The ruler, on the other hand, is an instrument used to measure all kinds of items and includes centimeters, millimeters, or inches. These can be found individually, or all together on a ruler. Most rulers are created from wood, while it is common for children of school age to have plastic rulers in all different colors.