The determination of the relative positions of two points by simultaneous Doppler satellite observations from each point.
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GRID TRACK
The direction of the track relative to grid north
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HELIOCENTRIC
Relative to the sun as a center
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FRICTION
The resisting force encountered at the common boundary between two bodies when, under the action of an external force, one body, moves or tends to move relative to the surface of the other.
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FRETTING
Wear phenomena taking place between two surfaces having oscillatory relative motion of small amplitude.
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HACK
A chronometer which has failed to meet the exacting require- ments of a standard chronometer, and is used for timing observations of celestial bodies, regulating ship's clocks, etc. A comparing watch, which may be of high quality, is normally used for timing celestial observations, the watch being compared with the chronometer, preferably both before and after observations. Sometimes called HACK CHRONOMETER.
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NATIONAL TIDAL DATUM EPOCH
The specific 19-year cycle adopted by the National Ocean Survey as the official time segment over which tide observations are taken and reduced to obtain mean values(e.g., mean lower low water, etc.) for tidal datums. It is necessary for standardization because of apparent periodic and apparent secular trends in sea level. The present National Tidal Datum Epoch is 1960 through 1978.
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TRIBOLOGY
The science and technology of interacting surfaces in relative motion, including the study of lubrication, friction and wear. Tribological wear is wear that occurs as a result of relative motion at the surface.
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GAS-OIL-RATIO (GOR)
The gas volume flow rate, relative to the oil volume flow rate, both converted to volumes at standard pressure and temperature.
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STATIC FRICTION
The force just sufficient to initiate relative motion between two bodies under load. The value of the static friction at the instant relative motion begins is termed break-away friction.
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VISCOSITY INDEX (VI)
A commonly used measure of a fluid's change of viscosity with temperature. The higher the viscosity index, the smaller the relative change in viscosity with temperature.
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