Nobody can become a violin virtuoso or a pianist solely by reading books on how to play the violin or the piano. For the same reasons, nobody can become an expert roll designer solely by reading this or any other book on roll pass design. This book, taken by itself, will never make a good roll designer of a stenographer or a store room clerk. What the book is intended to do and can do is to help a roll designer to do his work better and more intelligently. It can also help a man to become a roll designer, but not without practice, or, more strongly expressed, years of practice. The theories here explained, which are the result of fourteen years of experimental work, theoretical analysis, and classroom work with experienced roll designers, will keep him from many a mistake and will shorten the process of learning by experience.