If I have to play around with it, I think I will stick with Jamie Gritton's Backtester, and keelix.

It's not so much that you have to play around with it to find out what it does,
more that it's complex so you have to try things like doing homework to learn things better.
The documentation from Robbie is a bit scattered about, but it's quite rigorous.
(as with pretty much anything Robbie does)

Just search for posts mentioning gtr1 with author rgearyiii, sort descending by recs.

The best way to learn it is to go through the example screens
and compare the backtest.org or radiscript definitions to the corresponding gtr1 code.
The first few examples were done one post at a time by Robbie, and
they walk through the reasoning. Search for his posts containing the word "torpedo" .
Start with simple screens (RS26, then maybe YLDYEAR), work your way up.
Use High_Relavive_Value as your PhD thesis. The "rank" commands are the hardest to grasp.
http://boards.fool.com/highrelativevalue-not-torpedoed-25735...

The main starting points are
the examples http://members.iinet.net.au/~rgeary/example.html
The (incomplete but handy) field summary http://members.iinet.net.au/~rgeary/fields.html
The (almost entirely) complete glossary http://members.iinet.net.au/~rgeary/glossary.html
and the always-up-to-date-but-cryptic list:*.* parameter

Jim