TIDAL DATUM PLANES AS 
The heights of low water and lower low water vary in accordance with changes in 
sea level. Hence the low-water inequality, which is the difference between the heights 
of low water and lower low water, is independent of variations in sea level. This means 
that only the annual variation and the 19-year variation need be considered with regard 
to the diurnal inequality. These are of the same nature as the corresponding variations 
in lower low water, which were found to be due to changes in the relative positions of 
earth, moon, and sun. Factors for correcting monthly and yearly values of the diurnal 
inequality may therefore be derived from astronomical considerations, and in Table 6 
such factors are given for each month and year of the 50-year period 1931-1980 as com- 
puted from Tables 6 and 32 of Harris’ Manual of Tides. 
TABLE 6.—F actors for correcting diurnal inequality to mean value 
Year Jan. Feb. Mar. | Apr. May | June July Aug. | Sept. Oct. Nov. Dec. Mean 
OS ieee ree ea es 0.79 0. 91 1.03 0. 97 0. 82 0. 76 0.78 0. 91 1. 04 0. 96 0. 82 0. 76 0. 879 
GE eee 0.79 0. 91 1.03 0. 97 0. 82 0. 76 0.78 0. 91 1. 04 0. 96 0. 82 0. 76 0. 879 
TCE Es a ene a 0.79 0. 91 1.04 0. 98 0. 83 0. 76 0.79 0. 92 1.05 0. 98 0. 83 0.77 0. 888 
POG Apa teeta een ee a 0. 80 0. 92 1.06 1.00 0. 84 0.78 0. 80 0. 94 1.08 1.01 0. 85 0. 78 0. 905 
NOS ESS i eee 0. 82 0. 95 1.10 1.03 0. 87 0. 80 0. 83 0. 97 1.13 1.05 0. 88 0. 81 0. 937 
OS Gree aes et ens 0.85 1.00 i U5} 1.08 0. 90 0. 83 0. 86 1.01 1.19 1.10 0. 92 0. 84 0. 978 
TO EY. te he Oe 0. 88 1.04 22; 1.14 0. 94 0. 86 0.90 1.07 1. 26 1.16 0. 96 0. 88 1. 026 
TIGR AS Ee ae ee 0. 92 1.09 1.30 1. 21 0. 99 0. 90 0. 94 if 118} 1.34 i, 73} 1.01 0. 92 1. 082 
NOEs. ae eee 0.97 1.15 1.38 1. 28 1, 04 0. 94 0. 98 1.18 1. 42 1. 29 1.05 0. 95 1.136 
U9AQ eh eee Leer 1. 00 1 PAl 1. 44 11,683 1.07 0. 96 1.00 1. 22 1.47 1.33 1. 07 0. 96 1.172 
ROA par ees pees ie 1. 01 1, 22 1. 46 1.34 1.07 0. 96 1.00 1, 22 1. 47 1.33 1.07 0. 96 1.176 
TOO 2 tS eee 1.01 121 1. 45 il, $8} 1.07 0. 96 0. 99 1. 20 1.43 1.30 1. 04 0. 94 1.161 
O43 epee cs deat fe! 0. 98 1.18 1.39 1. 28 1.03 0. 93 0. 96 1.15 1. 36 1. 24 1.00 0. 91 1.118 
Gh Oe aa 0. 95 1.13 1, 31 UG PAl 0. 99 0. 89 0. 92 1.09 1. 29 1.17 0. 96 0. 87 1. 065 
1. 06 1. 23 1.14 0. 94 0. 85 0. 88 1.04 1. 20 1.10 0. 91 0. 83 1.007 
1.01 1.16 1.08 0. 90 0. 82 0. 84 0. 99 1.14 1.05 0. 88 0. 80 0. 962 
0. 97 1.11 1. 03 0. 87 0.79 0. 82 0. 95 1.09 1. 01 0. 85 0. 78 0. 925 
0. 94 1. 07 1.00 0. 84 0.77 0. 80 0.93 1. 06 0. 98 0. 83 0.76 0. 899 
0. 91 1. 04 0. 98 0. 83 0. 76 0.78 0. 91 1. 04 0. 96 0. 82 0. 76 0. 882 
0. 90 1.03 0. 97 0. 82 0. 76 0.78 0. 91 1. 04 0. 96 0. 82 0. 76 0. 878 
0. 91 1. 04 0. 97 0. 82 0.76 0. 78 0. 91 1.06 0. 97 0. 82 0. 76 0. 882 
0. 92 1. 06 0. 98 0. 83 0..76 0.79 0. 92 1.07 0. 99 0. 83 0.77 0. 892 
0. 94 1.08 1.01 0. 85 0.78 0. 81 0. 95 1.11 1. 02 0. 86 0. 79 0. 917 
0. 97 1.13 1.04 0.88 0. 80 0. 84 0. 98 1.16 1.07 0. 89 0. 82 0. 951 
1.01 1.19 1.09 0. 91 0. 84 0. 87 1. 03 1. 23 1.12 0. 93 0. 85 0. 994 
1.06 1. 26 1.16 0, 96 0. 87 0. 91 1.09 1.31 1.19 0. 97 0. 89 1. 048 
1.12 1.34 il, 2B} 1.00 0. 91 0. 95 Pay 1.39 1, 26 1. 02 0. 92 1. 102 
1.18 1.42 1. 29 1. 04 0. 94 0. 99 1. 20 1. 46 1. 32 1.05 0.95 1.152 
1. 22 1. 48 1. 33 1.07 0. 96 1.01 1.22 1.50 1.34 1.06 0. 96 1. 180 
1, 23 1.49 1.34 1. 07 0. 96 1.00 1. 22 1. 49 1.33 1.05 0. 95 1.178 
1. 21 1. 45 il oil 1.05 0. 94 0. 98 1.18 1. 43 1, 28 1. 02 0. 92 1.148 
1.16 1.38 25 1.01 0. 91 0. 94 2 1.35 i, PAL 0. 98 0. 89 1. 098 
1.10 1. 30 1.18 0. 96 0. 87 0. 90 1.07 a 27/ 1,14 0. 93 0. 85 1. 042 
1.04 1. 22 1.11 0. 92 0. 83 0. 86 1.01 1.19 1.08 0. 89 0. 82 0. 988 
0. 99 1.15 1. 06 0. 88 0. 80 0. 83 0.97 1.13 1. 03 0. 86 0.79 0. 945 
0. 95 1.10 1. 02 0. 85 0. 78 0. 81 0. 94 1.09 1.00 0. 84 0.77 0. 914 
0. 93 1. 07 0. 99 0. 83 0. 76 0. 79 0. 91 1.06 0. 98 0. 82 0. 76 0. 892 
0. 91 1.05 0. 97 0. 82 0. 76 0. 78 0. 90 1.05 0. 96 0. 81 0. 75 0. 879 
0. 90 1. 04 0. 96 0. 82 0.75 0. 78 0. 90 1. 04 0. 97 0. 81 0. 75 0. 875 
0. 91 1. 05 0. 97 0. 82 0. 76 0.79 0. 91 1. 06 0. 98 0. 82 0. 76 0. 884 
0. 92 1.06 0. 99 0. 84 0.77 0. 80 0. 93 1.09 1.00 0. 84 0. 78 0. 901 
0. 95 1.10 1.02 0. 86 0. 79 0. 82 0. 96 1.13 1. 04 0. 87 0. 80 0. 929 
0. 98 1.15 1. 06 0. 89 0. 82 0. 85 1.00 1.19 1.09 0. 90 0. 83 0. 967 
1.03 1. 21 1.12 0. 93 0.85 0. 89 1.05 1. 26 1.15 0 94 0 87 1.014 
1 09 1 29 119 0 98 0 89 0.93 if, Wil 1. 34 122, 0.99 0. 90 1.070 
1.14 1. 38 1. 26 1.02 0. 92 0. 97 il, aly 1. 42 1. 28 1. 03 0. 94 1.123 
1. 20 1.45 iL Bl 1.06 0. 95 1.00 1.21 1. 48 115883 1. 06 0. 96 1. 167 
1. 23 1. 49 1. 34 1. 08 0. 96 1.01 1. 22 1. 50 1,34 1. 06 0. 96 1. 183 
1. 22 1. 48 1.33 1.07 0. 96 1.00 1.20 | 1.47 1.31 1. 04 0. 94 1. 169 
1.19 1. 43 1, 29 1. 03 0. 93 0. 97 1.16 1. 40 1. 25 1.00 0. 91 1.129 
The factors for each month in Table 6 were computed for the middle of the month. 
In the last column the mean of the monthly factors for each year is given, and this may 
be taken as the factor for correcting the yearly inequality to a mean value. 
