Lettering is the process of forming letters, numerals, and other characters used in technical drawing. There are three main methods of lettering: freehand lettering done without tools, mechanical lettering done with tools like guides and templates, and modern drawing done with computer-aided software. The dimensions of letters are defined by their nominal size based on the height of uppercase letters, their center line which runs through the middle of each line element, and their lettering angle which can be vertical or inclined up to 75 degrees.