The Original 'JNT Height Database and Locator Conversion utilities
The source code is here
GEOSOURC.ZIP
and includes all the NGR / lat-long conversion maths. Also mouse control and graphics from pre-windows days.
Written in PowerBasic (16 bit for DOS)
NEWLOCTN.ZIP
A new Version of LOCATION with conversion to / from Natural Area Code (NAC) see
www.nacgeo.com/nacsite/
for details
GEOG2.ZIP
Terrain plotting and locator conversion software. Runs under DOS/Command Prompt. You will also need the Height database itself :-
HEIGHTS2.ZIP
which gives ground height above sea-level within the UK on a 500 metre grid based on NGR. Both files are needed.