"Tim Ward" wrote in message
...

Out of curiosity, what happens when you leave the instrument in the sun
and
the flask in the shade, and then alternately shade and unshade the
instrument? This seems like it would be more like what would actually
happen in the glider.

Tim Ward

I tried exactly this and saw no thermal response from the instrument at all.
The case appears to be made of a thick engineering plastic like Delrin. A
taut-band vario should be sensitive to changes in length caused by thermal
expansion but I didn't see any effect. The bellows and band are supported
on a brass frame inside the instrument that is carefully shaded from the
sun. I had been critical of the white face since it reflects on the inside
of the canopy but maybe I was hasty there. The white face may be useful in
controlling solar heating of the instrument.

Bill Daniels