In article ,
Stealth Pilot wrote:

if you were forced to use a gps unit for speed you could correct the
apparent value using the metrological forecast winds for the altitude.
it is a simple speed triangle calculation that could be done on a
circular sliderule like the jeppeson cr5.

The GPS unit could also derive the actual winds if you can fly a couple
of different headings at the same speed, or make a circle.
Glider-oriented GPS units typically do this automatically since it's so
useful to have and we tend to fly in circles all the time anyway.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon