envstat wrong: who's at fault?

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

I've got an i386 laptop on which envstat is printing out inconsistent
figures, and I'm wondering who's at fault (and, in particular, whether
it's something software can fix).

Specifically, here are the "acpibat0 discharge rate" and "acpibat0
charge" lines from several consecutive samples taken at one-minute
intervals:

acpibat0 discharge rate:     14.220 W
        acpibat0 charge:     47.320 Wh (90.20%)

acpibat0 discharge rate:     14.240 W
        acpibat0 charge:     47.060 Wh (89.71%)

acpibat0 discharge rate:     14.260 W
        acpibat0 charge:     46.740 Wh (89.10%)

acpibat0 discharge rate:     14.290 W
        acpibat0 charge:     46.410 Wh (88.47%)

acpibat0 discharge rate:     14.290 W
        acpibat0 charge:     46.110 Wh (87.90%)

acpibat0 discharge rate:     14.310 W
        acpibat0 charge:     45.850 Wh (87.40%)

The problem is that the charge is decreasing significantly faster than
the discharge rate indicates.  If the charge figures are accurate, the
discharge rate here is more like 18-19 W (eg, consider the third and
fourth data points above: (46.74 Wh - 46.41 Wh) / (1/60 h) = 19.8 W).

There is no real chance the "one-minute" intervals are significantly
different from one minute.  There is also no load to speak of, and, in
particular, no significant variation in load.  (While there is some
bursty load in that envstat is being run once a minute, the error that
would be expected to induce is in the other direction, because it would
mean that the discharge rate when sampled is higher than the minute's
average rate.)

The current software is 4.0.1, and one of the reasons I'm asking
whether this could be software is that that affects how plausible it is
that newer code might fix it.

If the measurements are likely to be noisy enough to account for this
and I probably just happened to catch an interval in which they were
underreporting the discharge rate, that's useful too.  One thing I have
not yet done is to plot the figures to see what they look like - I'm
letting the battery drain to the point of the machine going dead while
recording this information; once that's done I'll have some figures
worth plotting.)

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