http://www.geograph.org.uk/showmap.php?gridref=NZ305328
Double clicking the SU 109 941 bit on the second line cycles it between
SU 10923 94122, SU 1092 9412, SU 109 941 and SU 10 94.
Going from a ten to four figure GR
The E410923 and N194122 are the OS X and Y co-ordinates from the origin
somewhere to the south west of Land's End.
--
Phil Cook