Posted for Walter Atkinson <walter@advancedpilot.com>:

Lee:

To answer others, the DIF function is the difference between the hottest and
coolest EGT raw reading.

My best guess is that you had some sort of electrical spike.  Weird.  I
don't know of anything that could have caused this with the engine that you
would not have noticed in the cockpit.  That said, we've seen some weird
things happen with these electronic ignition/mag half and half setups.

Don't know for sure.

Walter Atkinson
Advanced Pilot Seminars