We use IGC track log files for competition and records because
basically they can not be edited and remain valid. They contain a checksum (
http://en.wikipedia.org/wiki/Checksum ), known as a G-record, that is check
to see that no editing has taken place.

The IGC file is a readable (sort of) text file and the G-record is at the end of
the file. This is what one looks like:

G28CCD9B26BBA6717E1F5DBB1FDC2D8D6

G78C2C5A7418E0F3DCE172C820103F0D3

GFA01E3F5475E4857FC73253400F61B50

G0000000000000000FFF100000A000000

If you down load your GPS or flight computer with GpsDump (
http://home.gethome.no/stein.sorensen/body_gpsdump.htm ) then it is easy to
check the validity of your flight. Just click on the menu, File, then Verify IGC
log from GpsDump.

But if you try to use GpsDump to check an IGC file that has been downloaded by
some other program you'll get this message:

The problem is that each different GPS download program creates its own unique
type of G-record and IGC files downloaded by each program must be check by
validation programs that are associated with that download program.

For example, if you download your Flytec 6030 or Brauninger Compeo+ you would
need to use the MS-DOS program vali-bra.exe or vali-fly.exe (two names for the
same validation program) to check the validity of the IGC file:

But there is even a better way.

There is an on-line validation program from the FAI. You’ll find it here:
http://vali.xccomp.org/

This Server is used to validate remotely IGC files submitted at
various Online Contest systems.

Click
validation
web form which will take you to:
http://vali.xccomp.org/vali-verbose.html

All you have to do is browse for your IGC file on your computer. You will get
this kind of response: