I found I seldom used the mechanical vario. After having a power
failure once and having to fly for a couples hours with only a
mechanical vario. I traded my Mechanical PZL in for a B40. The B40 is
electric but has a 9V backup and an Audio. I have had to use it once
and it works great. The other thing I like about it is the B40 has an
external averager switch. So when I am not using it as a Backup I
switch it over and use it as a Averager. I don't really need this as
my CNAV has an Averager as well. But it does let the B40 do double
duty.

My panel has ASI, B40, CAV across the top
and ALT, MNAV on the bottom.

You can see a photo of it at:

http://www.soaridaho.com/photogaller...006/index.html

You will need to scroll down a few photos to find it.

Brian
HP16T