Thanks for this idea. Three out of the four gliders have the ability to show ground speed, as well as an independent IAS from their SN-10s to cross-check their ASIs. Getting a ground speed value from the tow plane to compare to the tow plane ASI as well as the glider ground speed during flight is also doable. Not sure when we can do this, but I intend to try it!

-John, Q3

On Tuesday, November 12, 2013 10:45:33 AM UTC-5, soarin wrote:
[snip}
The next relatively calm morning put a handheld gps displaying ground speed
in the tow plane where the tow pilot can easily see it while towing. If
his indicated airspeed is notably different than what he sees for gps
ground speed, you have good grounds for a discussion. However if your
indicated airspeed was notably different then his gps ground speed, the
discussion may be go differently.
[snip]