60 U. S. COAST AND GEODETIC SURVEY 



and longitude of the place is unnecessary, and for a continuing series 

 the spaces for the beginning and ending of the observations may be 

 left blank. The height datum in the heading refers to the datum 

 actually used for the tabulation, which is generally the tide staff zero. 

 Standard time is to be used consistently throughout the year regard- 

 less of the fact that daylight-saving time may have been temporarily, 

 adopted in some localities. The hours of the day are to be numbered 

 consecutively from 0^ (midnight) to 23^^ (11 p. m.) to avoid the 

 necessity of using the terms "a. m." and "p. m." 



200. Checking time. — In the portable gage record, the hours are 

 indicated by the numbered vertical lines of the cross-section paper, 

 the hours being subdivided into 10-minute spaces by finer vertical 

 lines. The time as indicated by these vertical lines is to be compared 

 with the correct time as given in the comparative notes entered by the 

 observer. Assuming that the observer has corrected any clock error 

 at each visit to the tide station, any loss or gain may be prorated over 

 the period intervening between the visits unless there is evidence to 

 indicate that the loss or gain was not uniform. 



201. In the standard gage record the hours are indicated by short 

 horizontal lines made automatically by the time clock of the gage. 

 The hour begins at the instant the mark leaves the curve, the length of 

 the stroke having no significance. The time notes entered on the 

 record by the observer should be examined, and if it is found that 

 the difference between the correct time and the gage time does 

 not exceed 3 minutes at any time, the hour marks as automatically 

 made by the gage may be accepted as correct and marked accord- 

 ingly. In cases where the hour marks are appreciably in error due to 

 failure of the time clock to keep correct time, the total error indicated 

 by the time clock may be prorated among the hour marks effected on 

 the assumption that the time clock has lost or gained uniformly 

 between consecutive comparative notes. The marks are to be num- 

 bered cbnsecutively from (midnight) to 23 (11 p. m.), and the 

 numbering checked at each time note on the marigram. In order to 

 expedite the work, the numbering of the odd hours may be omitted if 

 desired. The beginning of each day at the hour should be marked 

 with the appropriate date, 



202. In cases where the hour-marking device has failed to work 

 the following method may be used : First, from the comparative time 

 notes ascertain the position on the curve of the nearest exact hour for 

 each note made during the period when the hour-marking device was 

 not functioning. This is done by laying off 1 inch on a piece of paper 

 and dividing it into 12 equal parts, the inch nieasured parallel to the 

 datum line representing 1 hour on the tide curve and each of the 

 divisions 5 minutes. The correct time of the point on the curve being 

 known, as indicated by a time note, the nearest exact hour is laid off 

 by means of this "time scale." Second, through the points thus found, 

 indicating the exact hours, draw lines perpendicular to the datum line 

 and extending across the paper. Third, prepare a "dividing scale" 

 from a strip of paper somewhat longer than the greatest distance 

 between the time notes on the marigram. On the edge lay off equal 

 divisions about 1%2 inches long. These divisions should be numbered 

 consecutively from 0^ to 23'' and repeated if necessary. This scale is 

 then adjusted obliquely between two consecutive cross lines passing 

 through the correct hour points so that the numbers on the scale will 



