On Thursday, December 14, 2017 at 5:00:23 PM UTC-5, John Foster wrote:
Why do so many gliders seem to have multiple varios? Is it that critical to have a back-up for this instrument? Do they often fail and leave you in "
the lurch"?

There is only one essential instrument for VFR and it lies between you ears.
a vario is next, with a vent to cockpit static if the TE gets plugged.

BTW, which Elec varios have an audible sink alarm; the old Cambridge audio was useless in sink as airspeed noise over 60-70 kts covered the LF tone.

In 1970, I built an analogue vario-computer with audio, head up speed to fly reader, TE comp etc..and audio rising tone in lift, and broken tone louder and rising in sink. Just what I needed , but the transducers gave trouble.

John F