constituent— One of tlie harmonic elements in a matliematical expression for tlie 

 tide-producing force and in co-responding formulas for tlie tide or tidal current. Each 

 constituent represents a periodic change or variation in the relative positions of tlie 

 Earth, Moon, and Sun. A single constituent is usually written in the form y = A cos 

 (at + cc), in which y is a function of time as expressed by the symbol t and is reckoned 

 from a specified origin. The coefficient A is called the ampUtude of the constituent and 

 is a measure of its relative importance. The angle (at + «) changes uniformly and its value 

 at any time is called the phase of the constituent. The speed of the constituent is the rate 

 of change in its phase and is represented by the symbol a in the formula. The 

 quantity oc ig the phase of tlie constituent at tlie initial instant from which the time is 

 reckoned. The period of the constituent is the time required for the phase to change 

 tIu"ough 360° and is the cycle of the astronomical condition represented by the 

 constituent. Further information on tlie harmonic constituents of the tide or tidal 

 current is provided in the Manual of Harmonic Analysis and Prediction of Tides 

 (Schureman, 1941). 



control tide stations— Tide stations presently being operated by NOS and scheduled for 

 continuous operation indefinitely as part of the National Tide Observation Network, 



correction— A quantity which is appUed to an observation or function thereof, to diminish 

 or ehminate the effects of errors and obtain an improved value of tlie observation or 

 function. It is also appUed to reduce an observation to some arbitrary standard. The 

 correction corresponding to a given error is of tlie same magnitude but of opposite sign. 

 The signs are given by the equation: improved value = observed value -i- correction. 



correction, adjustment (leveling)— A correction applied to an orthometric elevation to 

 produce an adjusted elevation, for eUminating the effects of circuit closures. 



correction, index (leveling)— A correction which must be appUed to an observed difference 

 of elevation to ehminate the error introduced into the observations when the zero of the 

 graduations on one or both leveling rods does not coincide exactly with the actual 

 physical foot or bottom surface of the rod. 



correction, level (leveling)— A correction applied to an observed difference of elevation to 

 correct for the error introduced when the Une-of -sight through the leveling instrument is 

 not absolutely horizontal when the bubble is centered in its vial. 



correction, orthometric— A correction appUed to a preUminary elevation to correct for the 

 error introduced when level surfaces at different elevations are not exactly paraUel. 



correction, rod (leveling)— A correction appUed to an observed difference of elevation to 

 correct for the error introduced when the leveling rods are not actually of the length 

 indicated by the graduations. 



correction, temperature (leveUng)— A correction appUed to an observed difference of 

 elevation to correct for the error introduced when the temperature at which the leveling 

 rods are used in the field is different from the temperature at which tiiey were 

 standardized. 



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