Garmin gpsmap 76s, glide ratio, airspace zone

Hi,
I'am not quite sure this is the right forum to post my question, let me try
(I also found some specific gps forums)

I just bought a garmin gpsmap 76s mainly for use in a glider (hence the post
in the current forum)

I wonder if someone has some experience with such device for two points.

First point: I bought it because it has interesting feature such as glide
ratio and glide ratio to target. The latter is perfect, but I found the
glide ratio function difficult to use or at least difficult to take
advantage of. The calculation seems to be done on instant value without any
"smoothing", as a glider moves a lot the result can vary from very low value
to glide ratio higher than 500!! within a couple of seconds. Have you
experienced such behavior? Is this a user error? A bug?

Second point: to draw airspace zone it seems possible to use waypoints and
routes. Do you know other possibilities? Using a mapsource format compatible
for instance

Thanks in advance for your answers
Gilles