Technology has brought us new ways of measuring.  Location was once determined based on astronomical observations and time (which was also based on astronomical events) then measured relative to the Prime Meridian Line in Greenwich London.  

 

Now things have changed but it is not widely advertised.  Time is now based on vibrations of atoms in an atomic clock and location is often based on measurements from man made satellites orbiting the earth and new mathematical equations.  

 

One effect of this is shown when using a GNSS receiver or Google Earth to locate the Prime Meridian which is the commonly known point of 0 Longitude.  

 

GNSS and Google Earth use the WGS84 ellipsoid (mathematical equation) to locate positions.  This places 0 degrees approximately 102.5m east of  the Prime Meridian at the Royal Observatory in Greenwich London as shown in the pictures below.

 

This is not a problem or any concern, it is just something to be aware of as proof that accurate positioning requires a bit more thought as to what you are trying to achieve.