Google Maps
An attempt to calibrate the longitude information from Google maps--it appears that the URL which can be obtained from "link to this page" contains ll=,and refers to the left edge of the displayed area.
Tue Mar 27 13:41:02 2007 - permalink -
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http://maps.google.com/maps?ie=UTF8&z=19&ll=51.477962,0&spn=0.001036,0.002398&t=k&om=1