Two L-NAV Questions

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