This is a converter for the British National Grid co-ordinate system. It uses Javascript and isn't finished yet. We've got also converters for UTM-coordinates and the Irish Grid.

British National Grid (1936)	coordinates	output accuracy 1 m 10 m 100 m 1 km 10 km 100 km
British National Grid (1936)	eastings (m)	northings (m)
Long, Lat (1936)	longitude λ (decimal deg)	latitude φ (decimal deg)
Cartesian (1936)	X (m)	Y (m)	Z (m)
Cartesian (WGS84)	X (m)	Y (m)	Z (m)
Long, Lat (WGS84)	longitude λ (decimal deg)	latitude φ (decimal deg)
Long, Lat (WGS84)	longitude deg min hemisphere E W	latitude deg min
Long, Lat (WGS84)	longitude deg min sec hemisphere E W	latitude deg min sec