On Jul 21, 10:45*pm, Jim Kellett wrote:
1. We have an older (Model 20) L-NAV that suddenly started reading ca.
2 - 2.5 kts "pessimistic". *This started, perhaps coincidentally,
perhaps not, right after we'd had it at a public display, making us
wonder if perhaps someone accidentally tinkered with some of the
settings. * We went back to the manual and checked all the calibration
screens, and couldn't detect anything wrong. *Any ideas about what
might cause this instrument to suddenly start reading "low"?? *FWIW,
with the power on and sitting on the ground, the vario reads ca. 3 kts
down, and the averager says -2.8.

2. Our old PC laptop at the field has died. *Can't find the source of
new Cambridge software to download to another PC or, better yet, to
one of our Mac laptops. *Again, anyone have a link to this software?

Jim Kellett

I'm sure an email to Gary Kamerer at Nielsen Kellerman will yield the
right answer, but in my experience, this is usually the sign of Bad
Things to come. You can start with the Calibrate function and try
to get the offset back to zero, by my guess is that you will run out
of adjustment. Here's the text from the manual on this:

e. [Variometer]
This screen shows the Variometer A/D reading. With no lift or sink,
the reading should be 511.
If is not, you may add or subtract an offset with the UP or DOWN arrow
keys. If the offset is
more than 40 counts, consider sending your unit to Cambridge over the
winter.

When this happened to me in the past, it required swapping out of one
of the main bits of magic.

P3