Nearby is a marker for the Greenwich prime meridian. However, for all practical purposes the real line of zero longitude is about 92 clicks east of that line. This micro marks the actual line of zero longitude according to the WGS84 system which GPS receivers all over the world use today.
Log only; please bring a pen.
Update 14/6/2015: (Again) a new cache has been placed.
*Congratulations to pelagori for being the First To Find Both This Cache And It's NY Cousin GC16YZN!*
***Thanks to hopmaniak for creating this nice banner!***