Shielding efforts

We continued our shielding efforts yesterday by putting an anti-static mat under
the computers and connecting that to a grounded electrical outlet. Took some
readings with a body voltage meter and found no difference in readings with or
without the anti-static mat. Disappointing. I wonder if the problem is with the
mat (wrong type, wrong brand? - it's an Eclipse ProsKit anti-static computer
mat) or with the splitter we're using, a kind of octopus plug for banana jacks).
Will probably try grounding the mat directly into the outlet without a splitter
next, but need a banana jack extension cord first.

However, while taking these readings we discovered something else. My
husband's G4 Powerbook, which previously, consistently clocked in at over
50,000 millivolts on the body voltage meter, was now reading between zero and
3 millivolts, with either myself or my husband holding the electrode with one hand
and then touching the laptop with the other hand. This was such a dramatic
change that we did a bunch of tests to make sure our multimeter was not
defective -- tested the battery, grounded the multimeter to several different
grounding sources in our home to make sure the ground was true, etc. As far as
we could tell the multimeter was fine.

FYI, this G4 laptop is the computer that has given my husband so much trouble
over the years -- breaks down constantly, but more than that, has been one of
his worst ES triggers. But, yesterday afternoon, he was able to touch it with his
bare hands and not get "zapped" (feel ill and exhausted). He said he also noticed
that it didn't feel "hot" to him.

Other notes:
1) Baseline body voltage reading -- just sitting in the workstation chair, not
touching any equipment, was now 300 millivolts; higher than when touching the
G4 Powerbook. (How can this G4 be reading LOWER than everything else around
it? The G4 tested lower than the peripheral keyboards, lower than the old G3
laptop...very puzzling.)
2) The only significant change that might explain the new low readings from the
G4 is that we recently grounded the electrical outlet that is this computer's
power source.
3) We took our G4 body-voltage readings at several times during the day, and at
one point, found the readings to be MUCH higher -- 1100 millivolts instead of
zero. (Which was still much lower than our initial, pre-grounded-outlet readings.)
We waited half an hour, took another set of readings, found the G4 to be at zero
again. Could not identify anything to account for the difference in the three sets
of readings.

So -- we don't necessarily have to understand why the G4 has suddenly decided
to be "friendly" (non-ES-trigger) but it would be nice if we could know that this
situation will remain constant. But maybe that's too much to hope for? Does
anyone have any idea what's going on here?

Thanks,
Cara