Data Network The data network offers another important means for enabling the user to perform his own calibrations, for when sufficient data have been obtained to characterize a substance, it then can serve as a reference material for the calibration of instruments that measure the properties of other substances. The use of freezing and boiling points of various substances the "fixed points" of the temperature scale-to calibrate a thermometer is a good example. Thus, in this network the NBS role is to select certain key materials, to characterize these materials carefully, and to make precise measurements of their properties. In some cases the Bureau makes available not only the data but the materials themselves as standard reference materials. The system can then couple to the properties of these materials and use them as points of reference in building a reservoir of data to meet the remaining needs. This central function provides a basis for NBS leadership of the system. At the same time it supplies the system with the basic information needed for self-calibration of instruments and measurement procedures, and gives scientists and engineers the data they depend on in designing and building apparatus and equipment. To do the job properly, NBS must obviously have broad competence in materials research and in measurement science. The corresponding data network for design specifications or performance characteristics of devices and systems is at present quite broad and diffuse. At this stage of the network's development NBS devotes its effort to providing the technical basis for setting meaningful design or performance standards, leaving the actual setting of the standards to the voluntary cooperation of the other elements of the system (except for mandatory standards that NBS is legally required to set). The data network is of great value in providing a basis for decisions that must rely on measurement. If, for example, an engineer were setting out today to design a new competitive light bulb, there are a great many things he would need to know. Obviously he would need instruments to make direct measurements of the diameter of the bulb, the pitch of the thread, the weight of the materials, the diameter of the wires, and so on. But once he had the capability of making these measurements in production, he would still be a long way from the design of a light bulb. He would need a vast store of such ready reference information as the electrical resistivity and spectral emissivity of tungsten and other competitive materials, the melting point and thermal expansion of glass-in fact, a whole library of data of this kind (which incidentally would also be of value to designers of vacuum tubes and other products). If he has to stop and measure all these properties, he will be investing substantial sums in a research program before he can start his design. On the other hand, if data are already available because someone else has already measured the properties, then he Graphic representation of interactions between various groups in the data network. can save this large investment. Once he has found the numbers, he can proceed with the design, provided that he can trust the numbers to be correct. There is a second important aspect which points up the need for critically evaluated data in the decision process. When an engineer goes to the literature in search of design data, he is likely to get a wide range of value for each property he looks up. If he is designing an industrial process that involves the heat of formation of hydrogen sulfide, for example, he will find in the literature an array of values ranging from 2,0 to 4.9 kilocalories per mole. If he accepts the value "2.0" for the heat of formation of hydrogen sulfide, he might conclude that his planned process will not work and there is no point in going further. On the other hand, if he accepts the value "4.9" he may find that his process will be highly productive and should be pushed. In the absence of critically evaluated data on the heat of formation of hydrogen sulfide, he can do only what is usually done in industry today--seek expert advice if he can find it, make an educated guess, or measure it again himself, adding another value to the list. Unless he is an expert in the measurement of heats of formation, the value he obtains will probably be no better than those already in the literature, and may be much worse. The solution to this type of problem is to assemble a group of experts who know the field and who can evaluate the various measurements from the literature and obtain a "best value"-the most acceptable and trustworthy value-and can make this value generally available. This is the process of critical data evaluation and compilation. In the data network the primary need is for a core of carefully measured key data that can serve as reference data for the determination of other data throughout the system. The process of critical evaluation and compilation of data has lagged far behind the generation of data in the literature. As a result, a large backlog of unevaluated data has been built up, and as this backlog continues to grow it has become increasingly difficult for scientists and engineers to find the data they need. Lack of critically evaluated data in conveniently available form has thus become an important and wasteful deficiency of the national measurement system. To remedy this deficiency, the Office of Science and Technology in 1963 established a National Standard Reference Data System and charged NBS with the responsibility for its administration and coordination. Techniques Network The techniques network is that part of the national measurement system through which all users of the system can be told how to make optimum use of the measurement capability developed in the instrument network and the data network. Thus the techniques network provides users with the procedures and techniques that make for meaningful measurement. The term "meaningful measurement" has two distinct aspects. The first is concerned with the ability to measure what one sets out to measure. For example, in attempting to measure the temperature of a particular body at a certain stage of a physical or chemical process, it is sometimes very difficult to be sure that one is in fact measuring the desired temperature, rather than some other temperature within the system. Even though the measurement may be very precise and reproducible, the temperature thus obtained may be quite different from the actual temperature of the body, and thus the measurement can be highly inaccurate. The other aspect of meaningful measurement is the matter of determining what one should set out to measure in order to accomplish a particular measurement goal. The problem is to find what properties, or combination of properties, or set of physical quantities can be measured, so precise and accurate indications can, by some agreedupon process, be put together to give a number characteristic of the aspect of the system being measured. It must then also be shown that the chosen procedure does in fact lead to an objective, reproducible measurement. To make meaningful measurements the materials involved must be characterized in terms of properties that are relevant to the measurement goal being sought and in terms of the environment in which the measurements are to be made. Characterization becomes more difficult and more sophisticated as the interactions of materials multiply and become more intricate, and as the environments become more extreme. Characterizing the bulk properties of a material for various measurement objectives is complex. And obviously the characterization of Graphic representation of interactions between various groups in the techniques network. materials in environments of plasma temperatures for example— where even the usual definition of temperature does not apply-is a great deal more difficult than doing so at more mundane temperature ranges. In this country an extensive network of institutions and organizations has grown up, aimed in one way or another at proper utilization of the national measurement system for the making of meaningful measurements. This techniques network has not yet been as well examined or understood as the instrumentation and data networks. At a minimum, it includes professional journals and other publications; meetings of professional societies; organizations and institutions that provide training in measurement techniques; standardizing bodies such as the USA Standards Institute, the American Society for Testing and Materials, and the International Standards Organization; standards of practice which include agreed-upon procedures for making measurements; and the educational institutions that provide the trained manpower to operate the national measurement system. As an institution which has developed the capability for leading the national measurement system, NBS has a responsibility for making available the information and know-how it has acquired in developing this capability. To fulfill this responsibility, the Bureau renders consultative and advisory services to standards laboratories, publishes data and information on measurement techniques, sponsors symposia and training courses on measurement topics, and cooperates extensively with standardizing bodies, particularly through participation of Bureau staff members in the committee work of these organizations. INSTITUTE FOR BASIC STANDARDS The Institute for Basic Standards (IBS), one of three institutes which comprise the National Bureau of Standards, has as its first responsibility the provision of "the central national basis for a complete, consistent system of physical measurement properly coordinated with those of other nations." As a second responsibility IBS develops and maintains standards for physical quantities and for the measurement of physical properties. In concert with the Bureau's Institute for Materials Research, IBS shares the responsibility for providing physical data on the properties of matter and materials. Implicit in the assignment of the first responsibility is the recognition that there does exist a national system of measurement and that this system is a centralized one, with a central laboratory which develops and maintains the national standards for physical measurement and provides the starting point for a chain of measurement leading from those standards to the ultimate users of the system. This chain. must provide for measurements of all necessary magnitudes, from the properties of atoms to those of the universe. From the point of view of the ultimate user who faces a measurement problem, such as finding the diameter of a ball bearing or the melting point of a metal, the measurement chain can operate in two different ways: (i) It can provide the user with a proven measurement technique or with a calibrated instrument, traceable back to the national standards, with which he can measure the diameter or the melting temperature. (ii) In the case of the melting temperature or other similar properties, it can provide him with an immediately available answer in the form of critically evaluated data which previous investigators have obtained in measurements based on the national standards. As the nation's central measurement laboratory, NBS exercises leadership in both these measurement areas. In the Bureau's laboratories the acquisition of standard reference data by precise measurement goes on side by side with research to develop and improve the national standards and associated measurement methods. PHYSICAL QUANTITIES The strength and utility of the national measurement system depend fundamentally upon the existence of a complete, consistent system of units and standards around which the system can develop. The In |