HISTORY tells us that measurement has been one of the principal foundations upon which the material progress of mankind has been based. It is only by carefully comparing or measuring the unknown in terms of some known quantity or unit that real knowledge is advanced. As our modern way of living increases in complexity and as our knowledge of science and technology expands, measurements and measuring equipment have progressively increased in diversity and in complication. Better measurements have vitally aided our progress in understanding physical laws, in designing and operating new and improved machines, and in automatic control of processes and operations. In all fields of applied arts and sciences, our rich store of knowledge is largely the result of our ability to measure.