The Codes provide test procedures which yield results of the highest level of accuracy consistent with the best engineering knowledge and practice, taking into account the cost of tests and monetary value of efficiency to industry. Performance of equip-ment is determined in part by measurements of physical quantities. A measurement consists of sens-ing a physical variable and translating this result into data that is either indicated or recorded. Analog data are indicated by the position of a pointer on a dial or by a point or line on a chart. Digital data are indicated by a visual display of numbers or by a numerical printout. Devices used to make measurements are called instruments but many de-vices called instruments must be used with additional components to measure certain physical variables and quantities. A millivoltmeter, for example, can measure voltage but a thermocouple must be used in conjunction with the voltmeter to obtain a temper-ature measurement.
