TIDAL DATUM PLANES : 17% 
The primary determination of mean lower low water below mean half-tide level 
at La Jolla from the 19 year series 1928-1946 is 2.73 feet. The six values determined 
in the last column of the table above thus differ from the primary value by not more 
than 0.02 foot. Incidentally it may be observed that the primary determination of 
DLQ at La Jolla is 0.92 foot. So that from a year of observations the mean value of 
DLQ, as shown in the next to the last column, is determined within 0.01 foot. 
Los Angeles and La Jolla are about 75 miles apart and their tides have ranges 
and inequalities much alike. It will therefore be instructive to take an example of 
tides having different ranges and inequalities and separated also by a greater distance. 
Neah Bay and Seattle, in the State of Washington are a little over 100 miles apart. 
At the former the mean range of tide is 5.62 feet and the low water inequality is 1.58 
feet, while at Seattle they are respectively 7.65 feet and 2.84 feet. For the 19 years 
1930-1948 mean low water below mean half-tide level at Seattle was 3.82 feet and mean 
DLQ 2.84 feet. 
Seattle Neah Bay Factors for corrections Neah Bay 
Year : 
LW below LW below : r MLW Mean MLLW 
DL DL LW DL "i 
HTL Q HTL Q Q peloy DLQ ser 
Feet Feet Feet Feet Feet Feet Feet 
NOB S Bae ste ees = 3. 85 2. 62 2. 89 1. 44 0. 992 1. 084 2. 87 1. 56 4, 43 
IYI) cre eae 3p Oil 2. 46 2. 93 Il, 35) 0. 977 eA 2. 86 1. 50 4. 36 
IQs as ae 3. 89 2. 46 2. 87 1. 40 0. 982 1.114 2. 82 1. 56 4. 38 
OA FES a 3. 87 2. 69 2 1. 50 0. 987 1. 056 2.73 1. 58 4. 31 
IQA GEE ees 2. 2 3. 82 2. 92 219 1. 65 1. 000 0. 972 2.75 1. 60 4, 35 
QA Sine By U0 3. 10 Decal i, 7 1. 013 0. 916 219 1. 60 4, 35 
From the 14 years of continuous observations at Neah Bay, the mean value of 
low water below half-tide level corrected to the epoch 1930-1948 is 2.82 feet and the 
mean value of DLQ is 1.58 feet, so that the mean value of lower low water below half- 
tide level is 4.40 feet. The derived yearly values in column 8 thus are correct to 
within 0.07 foot of the mean value, in column 9 they are correct to within 0.08 foot, 
and in the last column to within 0.09 foot. 
The fact that the comparison of La Jolla and Los Angeles gave more concordant 
values than the comparison between Neah Bay and Seattle is due in part to the lesser 
‘distance between the former pair of stations. In part too, it is due to the fact that La 
Jolla and Los Angeles have more nearly similar tides than Neah Bay and Seattle, 
evidenced by the values of the ratio of K,+0O, to M, for these stations in Table 4. 
In general it may be taken that a year of observations when compared with a 
suitable primary station will give mean lower low water below HTL correct within 
about 0.05 foot. 
Month.—To exemplify the determination of mean lower low water from a month 
of observations we may take again La Jolla and Los Angeles, and Neah Bay and Seattle 
taking every other month of the year 1946. 
