magnetic variation

Hmmm. I did find one once, but as I can't remember where, tis is only to
give you hope.
"karel adams" wrote in message
...
Every version of FS I have known has a file called MAGDEC.BGL
In FS2002 it is FS2002/SCENERY/MAGDEC.BGL
It's size has remained constant since 5.1 and I reckon
the contents haven't changed much either...
This file must contain data for magnetic variation
i.e. by reading this file it should be possible
to determine the magvar for a given longitude/lattitude.
Does anyone know how to do this?
In other words how is the data organised in the file?
Maybe a bit of code that actually reads this file?

Or is there a place on the web where the various
.BGL formats are explained?
Somewhere on flighsim.com praps?

TIA for any hint,
Karel Adams