Back to a few of the original issues. A big questionh would be just how
accurate the average volt nut needs the 732A to be? I once owned two
732A, one working normally, and kept hot 24/7, and one that needed some
work with the charging circuits and new batteries. My 3458A being newly
cal'd at Agilent in Colorado Springs, I matched the two 732As to the
3458A, then powered off the one with problems, worked on it off and on
over several weeks, then powered it back up. What I found was that the
one I worked on (after 48 hours warm-up) was within 0.2ppm of the hot
one and the 3458A. Over the next year, the drift got a little larger
among the three, but not by much -- a spread of about another 0.2ppm if
I remember right.
That's when I decided that since I wasn't going to try to be a standards
lab, shipping a 732A cold for cal was much easier and effective than
trying to do it hot, and I live about 30 air miles from Fluke in Everett.
Can you live with 1ppm uncertainty in your 732A? Some here obviously
can't, but I think many of us can and would be happy with that level of
accuracy -- certainly good enough to cal the various 6-1/2 digit meters
around, including the 3457 mentioned originally. And given my experience
of 732A stability, especially the good old ones that come on ebay and
the like, that 1ppm uncertainty is also a good check on the state of cal
of even the 8-1/2 digit boxes, which despite their resolution, are not
spec'd long-term for even 1ppm at 10V.
Best,
Dick Moore
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