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lib/Geo/Coordinates/OSGB/Background.pod  view on Meta::CPAN

the OS has always also printed a latitude and longitude `graticule' around the 
edges of the large scale sheets.  Traditionally these coordinates have been 
given in the OSGB36 model, but since 2015 the OS has been printing revised 
editions of Explorer and Landranger sheets with WGS84 coordinates instead.
The legend of my recently purchased copy of Explorer 311 has this paragraph under the 
heading `The National Grid Reference System':

=over 4

=item * Base map constructed on Transverse Mercator Projection, Airy Ellipsoid, OSGB (1936) Datum.
Vertical datum mean sea level. The latitude, longitude graticule overlay is on the ETRS89 datum 
and is compatible with the WGS84 datum used by satellite navigation devices.

=back

If your map does not have the last sentence you can assume that it shows OSGB36
latitude and longitude.  Of course, this change makes no difference to the grid
itself.

The differences between the OSGB36 and WGS84 models are only important if you
are working at a fairly small scale.  The average differences on the ground