III. DATA AND SERIES 



Yearly mean sea level is the arithmetic mean of a calendar year of hourly 

 heights. The hourly heights were either scaled directly from a marigram or obtained 

 from a digital output of an analog tide gage at each tide station. The tide gage, 

 usually located on a pier, continuously measures sea-level heights relative to the 

 land adjacent to the station location. The gage is connected to bench marks on the 

 adjacent land by precise second-order class I leveling. The bench marks are located 

 in bedrock whenever possible. 



Table 1 lists the 67 permanent tide stations used in this study by number, 

 name, and location (latitude and longitude). They are all operated by the National 

 Ocean Service. Of the 67 stations, 44 were in operation prior to 1940 and have very 

 few and short breaks in their measurement series. San Francisco dates from 1855 

 (Smith, 1980), and New York, Fernandina, and Seattle date from 1893, 1898, and 1899, 

 respectively. Table 2 lists the 44 station locations and the first complete year of 

 each series. Where the length of a break in a series is sufficient to invalidate a 

 yearly mean, the missing year is so listed. 



IV. TRENDS AND VARIABILITY 



Table 3 gives the relative apparent secular trend, its standard error, and 

 variability for the entire length of the series at each station. Apparent secular 

 trend is represented by the slope of a least-squares line of regression through the 

 yearly means. About two-thirds of repeated calculations of the apparent secular 

 trend will differ from the true apparent secular trend by less than the standard 

 error of trend. About 95 percent of repeated calculations of the apparent secular 

 trend will differ by less than two times the standard error of trend, and practi- 

 cally all repeated calculations will differ by less than three times the standard 

 error of trend. 



Variability is represented by the standard error of estimate, which is the 

 standard deviation from the line of regression. About two-thirds of the yearly mean 

 sea-level values will differ from the straight line of regression by less than the 

 variability (standard error of estimate). About 95 percent of the yearly mean 



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