66 U. S. COAST AND GEODETIC SURVEY 



should be to take the middle of a smooth arc covering an hour or 

 more during the high or low water period. It is not necessary to 

 actually draw such an arc, but the point at which a smoothed curve 

 would have reached its maximum or minimum should be estimated 

 as closely as possible. In determing the times of the high and low 

 waters to the nearest tenth of an hour it may be found convenient 

 to construct a small scale 1 inch long and divided into 10 equal parts 

 for use between the hour marks on the curve. An experienced tabu- 

 lator, however, will usually be able to estimate the tenth accurately 

 without the use of such a scale. 



216. Heights. — The high and low water heights are to be tabulated 

 in feet and tenths and should refer to a uniform datum throughout 

 the entire series of observations. In general the datum adopted for 

 the tabulation is the zero of the tide staff as originally installed at 

 the station, allowances being made for any subsequent change in 

 elevation. However, any other datum may be adopted for the tabu- 

 lations, but it is desirable that the datum be sufficiently low to avoid 

 many negative readings. 



217. When tabulating from a portable gage record, the heights may 

 be taken directly from the scale of the profile paper provided the 

 gage has been consistently kept adjusted to agree with the tide staff 

 readings, but allowances must be made for any material variations 

 from such an adjustment. 



218. When tabulating from the standard gage record, a glass scale, 

 graduated to conform to the scale of the record is used. A line is 

 ruled across the underside of this scale to correspond to the corrected 

 scale setting as computed on form 455 (pars. 205-212). The scale is 

 then moved along the record with this line in coincidence with the 

 datum line on the record, the heights as read on the scale being 

 referred directly to the desired datum. At any change in the adjust- 

 ment of the automatic gage, the scale setting must be changed to 

 accord with the new setting as computed in form 455. 



HOURLY HEIGHT TABULATION 



219. The hourly heights are tabulated in form 362 (fig. 26) . Unless 

 otherwise directed these heights will be tabulated in yearly series, 

 beginning with January 1 as the first day of each series. The days 

 are to be entered consecutively, 7 days to the page and using both 

 sides of the form, without regard to change in calendar months or to 

 the time of changing the tide roll. The side of the form having the 

 wider margin on the left side should be used as the first page of each 

 sheet. The "day of series" will be numbered consecutively through 

 the year, beginning with "1" for the first day of January. If any 

 part of the record is lost, blank spaces should be left for later interpo- 

 lation of the missing tides. As stencils are to be used in connection 



