https://www.willswing.com/glider-flight-testing-and-tuning

In order to be able to effectively tune your glider and evaluate
tuning changes, it is essential to have a comprehensive understanding of flight
test methodology and to conduct a thorough flight test of your glider before you
make changes and again after each change to evaluate the effect of the change.
We therefore begin with a discussion of flight testing.

The information presented here supplemental to the flight testing and tuning
information in your glider’s owner’s manual, so review that information as well.
You can find Wills Wing manuals at
https://www.willswing.com/support/manuals/