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instrument that indicates speed. A cable from an automotive speedometer is attached to the rear of the transmission of an automobile; the cable turns at a rate proportional to the speed of the car. In a very common type of speedometer the other end of the cable is attached to a simple magnetic device inside the speedometer. In response to the rotating cable, this device moves a needle along a calibrated dial to indicate the speed of the automobile. Another type of automobile speedometer uses centrifugal force and operates in a manner similar to a flyball governorgovernor,
automatic device used to regulate and control such variables as speed or pressure in the functioning of an engine or other machine. A governor may be an electric, hydraulic, or mechanical device, or it may employ some combination of electric, hydraulic, and mechanical
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. The airplane speedometer is called an air-speed indicator. A dial that registers the speed in kilometers or miles per hour is actuated by the wind pressure in a tube located where it is not affected by the air stream from the engine. The speed of a watercraft is frequently determined by means of a patent or taffrail log. In this device a small propeller, which is towed astern, revolves as it moves through the water, activating a calibrated dial aboard the vessel. In another type of marine speedometer a tiny fin projects from the hull below the waterline. The resistance of the water to the passage of the fin is converted on a dial into terms of speed in knots.



an instrument used in motor vehicles to measure the speed of travel and the distance traveled. The speed indicator of a speedometer is magnetically operated, and the distance counter (odometer) operates mechanically by means of rollers. In mechanically driven speedometers, both the speed indicator and the odometer are connected by means of a flexible cable to a set of reduction gears, one gear of which is driven from the driven shaft of the vehicle’s transmission. In electrically driven speedometers, the transmission’s driven shaft is connected to a contact breaker that functions as a pickup and converts direct current into three-phase alternating current. The frequency of the alternating current is proportional to the speed of rotation of the driven shaft. The current feeds an electric motor, whose rotor rotates at the same speed as that of the pickup.


Galkin, Iu. M. Elektrooborudovanie avtomobilei i traktorov, 2nd ed. Moscow, 1967.


An instrument that indicates the speed of travel of a vehicle in miles per hour, kilometers per hour, or knots.


a device fitted to a vehicle to measure and display the speed of travel


A pattern of lights displayed on a linear set of LEDs (today) or nixie tubes (yesterday, on ancient mainframes). The pattern is shifted left every N times the operating system goes through its main loop. A swiftly moving pattern indicates that the system is mostly idle; the speedometer slows down as the system becomes overloaded. The speedometer on Sun Microsystems hardware bounces back and forth like the eyes on one of the Cylons from the wretched "Battlestar Galactica" TV series.

Historical note: One computer, the GE 600 (later Honeywell 6000) actually had an *analog* speedometer on the front panel, calibrated in instructions executed per second.
References in periodicals archive ?
Speedometers are not 100% accurate either and neither are speed cameras, it should stay at the 10% margin.
But AA president Edmund King said: "We need alert, safe drivers checking the road ahead and adhering to the limits rather than paranoid drivers forever checking the speedometer to check they are 1mph above or below the limit.
Edmund King, AA president, said: "We need alert, safe drivers checking the road ahead and adhering to the limits rather than paranoid drivers forever checking the speedometer to check they are 1mph above or below the limit.
President of the Society Irish Motorists Louis O'Hanlon said: "The vast majority of new cars on sale in Ireland from this month will have metric only, or metric predominant speedometers.
Drivers should be looking at their speedometers and reading road signs anyway - it is the law of the land.
Domed polycarbonate crystal lenses are used on trip odometer speedometers and memory and internal shiftlite tachometers.
But farmers can unintentionally apply too much chemical if they don't realize their tractor speedometers are providing them with inaccurate readings--sometimes as much as 20 percent off.
Speedometers in particular vary widely in accuracy and speed of reporting.
It's because car speedometers normally read 2mph to 4mph above true speed while LGV speedometers linked to tachographs are very accurate.
Many of the toys sold do not have speedometers and are being driven up and down housing estates.
They claim that motorists are too busy watching their speedometers and scanning for cameras to concentrate on road hazards.