Thanks Andy and all for the replies, I have some more reading to do but may take one of you up on your generous offers.   Very cool idea on the traveling reference!  Not sure I can contribute anything towards the project since my only "good" meter is a recently calibrated 3456A, but may just have to see about getting in on that!  I finally registered on EEVBlog, lots and lots to see and learn there.   In the meantime...  Far as differential voltmeters go for this level of accuracy, is a Fluke 893A really worth going to the trouble of overhauling, or should I keep my eyes open for something just a little better?  I have two of these units, one basically works but is inaccurate, the other has no meter deflection.  The reference diode would likely be a candidate for improvement, but wonder if the rest of the instrument could really take advantage of it.  Thinking thst something a little better, or perhaps just getting/rebuilding a 335A/D would be better bet than the 332B with an external differential meter.   Open to all thoughts, comments, and set-me-straight-isms! Regards, Chris  Sent from my SMRTphone -------- Original message --------From: Andy Lawrence <dr.diesel@gmail.com> Date: 8/12/17 7:44 AM (GMT-06:00) To: Discussion of precise voltage measurement <volt-nuts@febo.com> Subject: Re: [volt-nuts] 3458A in the SW Chicagoland area/Geller Labs references? If for some reason the US Cal Club doesn't fit for you: My parents live north of Chicago in Lindenhurst, and I *might* be visiting there for X-Mas this year.  Or if you get really motivated I live in Terre Haute IN, which is probably only 3 hours south of you.  Only one point of history but I have two recent cal'ed 3458As and a 731B. BR Andy On Fri, Aug 11, 2017 at 6:51 PM, Jason Pepas <jasonpepas@gmail.com> wrote: > Hi Chris, > > You might consider taking a look at the EEVBlog USA Cal Club thread.  We > are mailing a Geller Labs reference around the country. > > The reference doesn't have a lot of history built up yet, and we haven't > tried shipping it back and forth between the same two parties multiple > times to characterize shipping-induced instability, but it has been in the > hands of a couple of 3458A owners, so its uncertainty is a bit of a mixed > bag at the moment. > > Either way, its fun to participate :) > > http://www.eevblog.com/forum/metrology/usa-calibration-club/ > > -Jason Pepas > > > On Fri, Aug 11, 2017 at 4:55 PM, Chris Farley via volt-nuts < > volt-nuts@febo.com> wrote: > > > Greetings all, > > > > As suggested several months ago, I'm put out an inquiry/request to see if > > there's anybody in the area who has an HP3458A or better anywhere near me > > down here in Sandwich, that I might be able to either A) compare readings > > to my 3456A, or possibly use (without removing from your premises, > > obviously) use to calibrate my Fluke 332B.  I have means to keep my units > > powered during transport, so hopefully would not require hours of sitting > > to stabilize before taking any readings.  The 3456A's limitations are > > really being stretched, in trying to calibrate a 332B with it alone. > > > > Alternatively, is anybody aware of a Geller Labs (closed) voltage > > reference available on the used market, or something of equal or better > > precision available today?  The Malone Electronics VREF10-003 looks very > > interesting, with supposed 6mos accurace of ±300uV. > > > > Regards, > > Chris > > _______________________________________________ > > volt-nuts mailing list -- volt-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > > mailman/listinfo/volt-nuts > > and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/volt-nuts > and follow the instructions there. > -- projecthuh.com Never underestimate the carelessness of boredom... Most people prefer Windows because most people are idiots... _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.