The production of sheet metal parts and units depends largely on the skill of the craftsman in accurately performing hand processes, machine processes, and measurement and layout work. To develop these skills, it is important for the beginner to be able to solve everyday trade problems quickly and accurately. Arithmetic and mathematical principles are described in this text in a series of units to aid you in developing these skills. Each new principle is applied in one or more illustrative problems. Examples of these problems are broken down into step-by-step descriptions for ease in interpreting and understanding. They contain the information needed to work the mathematical problems included in the assignment portion of the unit. The knowledge gained in studying these principles and working the problems will be a definite asset to you when you are required to make a practical application of them on a specific job.