MANUAL OF TIDE OBSERVATIONS 



75 



not already computed, may be assumed to be less than 0.2 without 

 material error. For stations along the Gulf of Mexico from Key 

 West to the Rio Grande the mean range of tide is very small and the 

 correcting factor may be omitted. For stations on the Pacific coast 

 the value of the ratio may be computed either from the inequalities 

 or from the harmonic constants but need be carried to only one 

 decimal place. If this ratio is larger than 2.0, no correction need be 

 applied to the mean range. 



Factor F (Mn).—^or reducing the observed range of tide to its mean value 



Factor Fi. — For correcting DHQ and DLQ 



240. Comparison of simultaneous observations. — For a short 

 series of observa'tions, reduction by comparison of simultaneous ob- 

 servations is generally the best method provided there is a suitable 

 standard tide station from which the necessary simultaneous data may 

 be obtained. For this purpose the standard station should be so situ- 

 ated that the effects of meteorological conditions may be expected to 

 be similar to those at the station for which the results are sought. A 

 reference to the use of this method in computing lunitidal intervals 

 has already been made in paragraph 233. The process is especially 

 valuable in the reduction of the heights of the tide. For observations 

 covering a period of less than 1 month, form 248 is generally used, but 

 for series extending over longer periods, form 657 for the comparison 

 of monthly means will be found more convenient. The latter form 

 is self-explanatory. 



