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1. a device to attract attention, such as the pointer of a gauge or a warning lamp
2. an instrument that displays certain operating conditions in a machine, such as a gauge showing temperature, speed, pressure, etc.
3. a device for indicating that a motor vehicle is about to turn left or right, esp two pairs of lights that flash when operated or a pair of trafficators
4. a delicate measuring instrument used to determine small differences in the height of mechanical components. It consists of a spring-loaded plunger that operates a pointer moving over a circular scale
5. Chem
a. a substance used in titrations to indicate the completion of a chemical reaction, usually by a change of colour
b. a substance, such as litmus, that indicates the presence of an acid or alkali
6. Ecology
a. a plant or animal species that thrives only under particular environmental conditions and therefore indicates these conditions where it is found
b. a species of plant or animal whose well-being confirms the well-being of other species in the area





an instrument, device, or element that represents the progress of a process or the state of an object under observation and its qualitative or quantitative characteristics in a form convenient for human perception. Indicators may be of the visual, acoustic, or tactile type, depending on which sense organs are affected by the signal. Since 90 percent of all information is perceived visually by man, visual indicators are used most often, acoustic indicators less frequently, and those affecting the sense of touch (tactile) or smell, among others, least often. Sound indicators are used in the case of poor visibility, when the visual perception of the observer is overloaded with information, or when the observer’s attention is distracted from the visual indicator. Tactile indicators are usually used in conjunction with visual indicators if an exceptionally quick reaction to the incoming signals is required. In chemistry, substances that indicate the presence of a chemical reaction or change occurring in a medium under analysis are called indicators.

Signal indicators, in the form of simple devices such as signal lamps, bells, or levers, are installed most frequently. Colors are used to represent two or three clearly discernible states: green (process is operating normally—permission), yellow (demands increased attention of the operator or observer—caution), and red (process is disrupted—danger). Also used are the differences in brightness (blinking turn signal on an automobile; brightened knobs on a panel) or position, for example, a switch handle. Commands or quantitative data are communicated by means of signal lamps inscribed with numerals or legends. If reliable perception of the visual signal is required, it is supplemented by an acoustic signal (bell, howler).

Needle indicators, with a scale graduated in minutes, meters, kilograms, degrees, and the like, are used for indicating precise numerical values of the quantities being measured or controlled, such as time, distance, direction, velocity, consumption, or temperature. In addition to absolute values, needle indicators can also reflect the qualitative information expressed by the relative speed of the motion of the pointer (needle) or its position on the scale. Digital indicators, which provide rapid readings if precise quantitative data are required by the operator, are made in the form of rotating drum-type counters, projection of indirect lighting instruments, or matrix panels. Needle and digital indicators are combined to increase the limits or accuracy of measurements. The combination of several types of displayed information in one device provides the operator with an overall picture, shortening the time required for the distinct perception of its separate parts.

Graphic (visual) indicators depict the position of an object in space and the change of characteristics in the form of a graph or a curve on the screen of a cathode-ray tube. Projection indicators, which consist of a projection device and a screen, reflect complex and multiform information. Integrated displays also exist for the visual reproduction of the state and principal characteristics of a process directly on an operator’s screen (graphic display panel) or control panel. The perception of information is facilitated by the use of visual indicators that create a realistic effect. For example, in an instrument landing device the eight separate position indicator readings of an aircraft coming in for a landing are replaced by a single visual, though arbitrary, representation of the object’s movement on a screen. The direction of movement is indicated in the form of a ribbon moving to the horizon, the ribbon being divided by dark transverse stripes that, during the movement of an object, shift as if rushing toward the operator. The operator attempts to hold the moving object on the “road” lying before him. The main virtue of such indicators is that the operator perceives complex information directly, without intermediate transformations.

Indicators are widely used in scientific research, engineering, and everyday life. They indicate emergency situations and the arrival of particularly urgent information, facilitate decision-making, and serve as one of the principal methods of data communication between man and machine.


Lomov, B. F. Chelovek i tekhnika. Moscow, 1966.
Elektronnye sistemy olobrazheniia informatsii. Edited by J. Howard. Moscow, 1966. (Translated from English.)
Woodson, W. E., and D. Conover. Spravochnik po inzhenernoi psikhologii dlia inzhenerov i khudozhnikov-konstruktorov. Moscow, 1968. (Translated from English.)
Poole, H. Osnovnye melody i sistemy indikatsii. Leningrad, 1969. (Translated from English.)



(computer science)
A device announcing an error or failure.
A cathode-ray tube or other device that presents information transmitted or relayed from some other source, as from a radar receiver.
An instrument for obtaining a diagram of the pressure-volume changes in a running positive-displacement engine, compressor, or pump cylinder during the working cycle.
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