For the sake of clarity, as I continue to describe the readings, we're going to pretend that stage 2 really did read 0.01000v and not 0.00950v.
With that in mind, the device was configured to send 1000pa to the picoammeter, which should read it as 1.0v exactly. Instead, it reads a
negative 0.9611:
[ Attachment Invalid Or Does Not Exist ]
which, except for the change in sign, is consistent with the actual (non-pretend) stage2 voltage reading.
[I would show a photo here, but the forum just now started to block my photo uploads. I guess they're too big for its liking. So, no more photos.]
I'm not sure why it reads negative, but I do have a switch-polarity button, so I push that and continue with the measurements.
Anyway, long story short, I then went on to take the following measurements:
What should be 500pa reads as 0.47930 volts (again, consistent with the actual stage 2 division).
10pa, 8.749mv
4pa, 2.5mv
2pa, 0.8mv
0pa reads as 0.6mv, so it seems something is wrong with that measurement.
Now, importantly, even though this was supposed to be the bulletproof enclosure test setup, I'm *still* able to influence the DMM millivolt readings by moving my hand toward the test enclosure, even when it is closed up. So, go figure.
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif.pagespeed.ce.5xOqKkq0Co.gif)
Nonetheless, I seem able to get decent DMM measurements down to about 4pa, which means I can now read most of the single digit picoamps. At this point, to go further, I see no choice but to put the DMM inside the enclosure to do its measurements. Either that, or just be happy that it's doing as well as it seems to be.
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/xwink.gif.pagespeed.ic.cldandycH0.png)