You should look a the 90-05.html Web page at my Web site. It explains this tide crest and trough averaging technique in detail with drawings etc. Only crest and trough longitude data are used. And the locations where the two ocean crest and trough locations are determined for are in the Los Angeles and Christmas Island areas. The Solid Earth Tide locations are calculated for 75W and 0N. Using different locations like that is necessary becasue tide crest and trough locations largely depend upon where the measurements are made.