On Thursday, December 14, 2017 at 5:19:27 PM UTC-5, Roy B. wrote:
John:
This is a subject on which experienced glider pilots will disagree on. Many now use electronic instruments exclusively, in which case a single good vario is the norm. Others - who have doubts about battery sustainability (especially on long flights) will want a mechanical back up. I've had batteries fail very far from home and was happy to have a mechanical vario backup.. Or it may depend on your OCD medication level . . .
Roy

Let's talk politics - it's less controversial.

But seriously, I've always liked having a good (simple) mechanical vario backing up whatever electronic wizardry is the flavor of the month/year. I do from time-to-time like to compare readings, response rates, etc. just to make sure the morons, the neurons, and fig-newtons in the electronic instrument are behaving. In fact, I discovered a hardware/software problem this year when I started to notice consistent differences between the two instruments.

In 30 years of XC gliding, I'd say I've actually had to rely on the mechanical backup maybe 3 times when the electrics went south. Not exactly a compelling reason, but we're creatures of habit.

Erik Mann (P3)