The letters found on the body of the pencil denote what their intended uses are for. Each of the college pencils has a slider that shows which weight of lead you have in your pencil. Many of the pencils have a retractable sheet, meaning that the pencil tip fully retracts into the pencil's body. The range of lead sizes was established for reproduction scale. This means that if you draw a large drawing that you are intend to shrink down, line width is very important. For example, if you draw with a .5 mm it will shrink to a .25 mm – scaling your lines precisely.