TIDAL DATUM PLANES 35 
TaBLe 2.—Day of series, page, and column for hourly height tabulations beginning January 1 
Common year Leap year 
Month - Page Column ee Month Page Column Pay ot | 
Venn toss ayaa 1 1 1 Vay lees Le 1 1 i 
]itelo) 1 oer een 5 4 32 186) ova eee ey oe 5 4 32 
JY ese Tl 9 -4 60 UN [Caria [esterases 9 5 61 
POs dle 13 7 91 HX) 0) tesa (nate Meee ee a 14 1 92 
iteinyaibiess ot a 18 2 all Neil sees eee 18 3 122 
ATU ES ise oe 22 5 152 fbn aes Le eo i are DP 6 153 
Uys 1 ee ee 26 a 182 Uiiliy eee Y 27 1 183 
ANUYGR, lus SSSI ec 3l 3 213 AO Ae ese aye 31 4 214 
NSS) Ole ee 35 6 244 Sept: leer 35 7 245 
Ocirellaws oe 2s 40 1 274 Oca e ae ee ane 40 2 275 
INOS aes 44 4 305 ANION Gul oe 44 5 306 
Decry lene sn oe 48 6 335 TD Yeo sl eae ae ee 48 7 336 
IDExO5, 3 eee 53 1 365 Dec Silee ea ste 53 , 2 366 
LJ 
for the month the mean value of sea level for the month is entered, as shown on 
Figure 15. 
After the tabulation of the hourly heights is completed, the high and low waters are 
tabulated. A specimen sheet of the tabulated high and low waters for the last half of 
June 1944 is shown in Figure 16. The first half of the month is tabulated on the other 
side of the tabulation form. 
In tabulating the high and low waters, the tabulator notes in succession the highest 
and lowest points of the tide curve, tabulating the times to the nearest tenth of an hour 
_ and the heights to the nearest tenth of a foot read directly from the cross-section paper. 
However, with tides of small range, it is better to tabulate the heights to the nearest 
half-tenth or even to the nearest hundredth of a foot. 
It is important to note that in determining the points of high and low water on the 
tide curve, which points give the times and heights to be tabulated, attention is to be 
centered on an arc of the curve that covers a time interval of about an hour each side of 
the high or low waters. The highest or lowest part of the smooth arc is chosen for the 
high or low water and not merely the highest or lowest point on the curve, which may 
be due to wave action or other disturbing factors. This matter will receive further con- 
sideration in connection with the discussion of irregularities in tide curves. 
In tabulating times to the nearest tenth of an hour and heights to the nearest tenth 
of a foot, provision must be made for the tabulation of values which lie exactly half way 
between tenths. For example, 8.25 hours may be tabulated either as 8.2 or 8.3 hours 
and, likewise, 6.75 feet may be tabulated as 6.7 or 6.8 feet. Obviously, some definite 
rule is desirable for such cases. A rule sometimes used is to drop the last figure, but this 
introduces a systematic error. A much better rule in such cases is to make the first 
decimal place even; for example, 8.25 would be tabulated 8.2 while 8.35 would be 
tabulated 8.4. ae 
When the tabulation of high and low waters for a calendar month has been com- 
pleted, the heights of the high and low waters are summed and the average values for 
the month derived. As shown on Figure 16, there are spaces provided for deriving the 
