One of the tendencies in measurement technology development is the development of measurement systems. By the measurement systems, we refer to a set of material and organizational resources, as well as programs for information processing, aggregated in order to obtain, transmit, and process measuring data, and to display and store them. The measurement system is equipped with a PC computer or a microprocessor chip; its task is to control information flow in the system, to process measuring data, and sometimes to store them. The computer or the microprocessor chip is a system controller, that is to say, a device managing the system. The measurement systems described in this book are exclusively digital systems. Measurement systems with the personal computer (PC), named computer-based measurement systems, are of great importance. Considering the widespread use of PCs in both industrial and research measuring laboratories, the building of a computer measurement system usually does not imply the purchase of a separate computer, but allows the utilization of the existing ones. This is especially important and economically effective in the case of building up computer measurement systems for the realization of temporary measuring tasks. Separate classes of computer measurement systems are the simplest two-component systems, composed of one measuring instrument plus one computer as the system controller. It is self-evident that the possibility of applying an existing computer for setting up the simplest measurement system decreases construction expenses of such a system considerably.