Measurement, a sequence of experimental and computational operations carried out in order to find the value of a physical quantity that characterises some object or phenomenon. A measurement ends with a determination of how closely the value found approaches the true value of the quantity (if there is no a priori information about this).
Measurement is the chief means of objective knowledge of the surrounding world. A complete measurement includes the following elements: the physical object (phenomenon) whose property or state the measured quantity characterises; the unit of that quantity; the technical means of measurement, graduated in the chosen units; the method of measurement; the observer (recording device) who perceives the result of the measurement; the value obtained for the measured quantity and the estimate of its departure from the true value, that is, the error of measurement. The value found for the measured quantity is the product of an abstract number (the numerical value) and the unit of that quantity. The estimate of the error is expressed in units of the measured quantity or in relative units.
A distinction is drawn between direct and indirect measurements. In a direct measurement the result is obtained immediately from measuring the quantity itself (measuring the length of an object with a graduated rule, for example, or the mass of a body with weights). Direct measurements, however, are not always possible or accurate enough. In such cases indirect measurements are used, in which the value sought is found from a known relation between it and quantities that are measured directly. The connections and quantitative relations that science has established between physical phenomena of different natures have made it possible to create a system of units covering every field of measurement. (see International System of Units). Measurement is to be distinguished from counting and from other ways of characterising quantities numerically, used where there is no one-to-one correspondence between a quantity and its numerical expression in definite units. Determining the hardness of minerals on the Mohs scale, for instance, is not to be regarded as a measurement.
Every measurement is inevitably attended by errors. According to the sources of the errors of measurement, a distinction is drawn between method errors, which arise from the imperfection of the method of measurement, and instrumental errors, which are due to the imperfection of the technical means used in the measurements. According to the way they show themselves, a distinction is drawn between systematic errors, which vary in a regular way or stay constant during the measurement, and random errors, which vary at random (because of the internal noise of the elements the measuring instruments are built from, uncontrolled random fluctuations of the ambient temperature and other influence quantities). In high-precision measurements systematic errors are eliminated by applying corrections. Random errors are estimated from the data of repeated observations by the methods of mathematical statistics. A problem of its own is the determination of the errors of measurement caused by the inertia of the measuring equipment used, when quantities that vary in time are measured. In the microworld the limit of attainable measurement accuracy is set by the uncertainty relation.
Securing the uniformity of measurements in the country is the task of the metrological service, which maintains a state of measurement in which the results are expressed in legally established units and the errors of measurement are known with a specified probability. The measures for securing the uniformity of measurements include the keeping of the measurement standards of the units, the verification of the measuring equipment in use, the development of methods of determining the errors of measurement and so on. The certification and standardisation of measurement procedures are coming into ever wider use. (GOST 8.010—72), including state standardisation (GOST 8.346—79, 8.361—79, 8.377—80 and others). The ways of presenting measurement results and the indices of measurement accuracy are laid down in GOST 8.011—72.
Measurement is the chief means of objective knowledge of the surrounding world. A complete measurement includes the following elements: the physical object (phenomenon) whose property or state the measured quantity characterises; the unit of that quantity; the technical means of measurement, graduated in the chosen units; the method of measurement; the observer (recording device) who perceives the result of the measurement; the value obtained for the measured quantity and the estimate of its departure from the true value, that is, the error of measurement. The value found for the measured quantity is the product of an abstract number (the numerical value) and the unit of that quantity. The estimate of the error is expressed in units of the measured quantity or in relative units.
A distinction is drawn between direct and indirect measurements. In a direct measurement the result is obtained immediately from measuring the quantity itself (measuring the length of an object with a graduated rule, for example, or the mass of a body with weights). Direct measurements, however, are not always possible or accurate enough. In such cases indirect measurements are used, in which the value sought is found from a known relation between it and quantities that are measured directly. The connections and quantitative relations that science has established between physical phenomena of different natures have made it possible to create a system of units covering every field of measurement. (see International System of Units). Measurement is to be distinguished from counting and from other ways of characterising quantities numerically, used where there is no one-to-one correspondence between a quantity and its numerical expression in definite units. Determining the hardness of minerals on the Mohs scale, for instance, is not to be regarded as a measurement.
Every measurement is inevitably attended by errors. According to the sources of the errors of measurement, a distinction is drawn between method errors, which arise from the imperfection of the method of measurement, and instrumental errors, which are due to the imperfection of the technical means used in the measurements. According to the way they show themselves, a distinction is drawn between systematic errors, which vary in a regular way or stay constant during the measurement, and random errors, which vary at random (because of the internal noise of the elements the measuring instruments are built from, uncontrolled random fluctuations of the ambient temperature and other influence quantities). In high-precision measurements systematic errors are eliminated by applying corrections. Random errors are estimated from the data of repeated observations by the methods of mathematical statistics. A problem of its own is the determination of the errors of measurement caused by the inertia of the measuring equipment used, when quantities that vary in time are measured. In the microworld the limit of attainable measurement accuracy is set by the uncertainty relation.
Securing the uniformity of measurements in the country is the task of the metrological service, which maintains a state of measurement in which the results are expressed in legally established units and the errors of measurement are known with a specified probability. The measures for securing the uniformity of measurements include the keeping of the measurement standards of the units, the verification of the measuring equipment in use, the development of methods of determining the errors of measurement and so on. The certification and standardisation of measurement procedures are coming into ever wider use. (GOST 8.010—72), including state standardisation (GOST 8.346—79, 8.361—79, 8.377—80 and others). The ways of presenting measurement results and the indices of measurement accuracy are laid down in GOST 8.011—72.