It has been well said that "the man in whose brain the manufacturing system was born was he who first took a piece of scrap iron and drilled two holes in it, to guide a drill in making another piece with two holes in it the same distance apart as in the first piece." The men who now fill our drafting rooms and tool rooms, and who devise and construct tools for the production of interchangeable metal parts, are his descendants. They have made possible the manufacture of the breech─loading gun, the typewriter, the cheap sewing machine, the cash register, the machine─made watch, the automobile, as well as a thousand and one other mechanical articles, machines, and devices which form an integral part of our twentieth─century civilization. To render these systems efficient and economical for these purposes, the work must be _repetition or duplicate work_. That is, there must be very large numbers of each of the different parts; and to carry out the scheme of operation for the division and subdivision of work; a single operation on a large number of parts is performed; then the work is handled again, perhaps in another machine, and another operation is performed; and so on until the part is complete. Thus a piece of comparatively simple form may require a large number of separate and distinct operations to complete it. But, as each single operation is performed by one operator, he may give his undivided attention to the accuracy of that operation; hence very accurate work can be produced. [Illustration: A MACHINE SHOP WITH GALLERIES AT THE SHIPBUILDING PLANT OF THE GAS ENGINE & POWER CO. AND CHARLES L. SEABURY & CO., CONSOLIDATED] In the development of these systems, the work has continually grown more and more complex, as have also the requirements as to the buildings in which manufacturing work is performed, and as to the equipment necessary to perform it. Conditions have been continually changing; greater speed as well as greater accuracy in all machine operations has been demanded; and a largely increased output per employee has been required. So great and urgent has been this demand that the employee of to─day will turn out from three to ten times the volume of product of a given kind that he did only a few years ago. Undoubtedly this result has been brought about in great measure by the great improvement in machines, tools, and fixtures. Much is also due to the use of tools composed of high─speed steel; still more, to the employment of improved systems for handling work.