For the Allan variance, I could use the program if you provide some data (e.g. CVS data in some form, e.g. zip compressed).
I found the software on TiN's xdevs server - if you dare. https://doc.xdevs.com/docs/_Freeware/
I'll trust a download from TiN's server much more than I would allowing some dodgy website's Javascript, that's for sure! Anyway, I'll be installing it into a Windows virtual machine, so I'll just take a snapshot of the VM before installation, run it, and then revert the snapshot afterwards. Thanks for the detective work!
I think Dek's machine still has some more serious problems to be found. Mine might have an unwanted offset on DCI, but it can be nulled out and the meter would have passed calibration on the DCI range without adjustment if it wasn't for the unwanted offset at 0 on DCI.
You're right about testing the reference voltages of course - just connect the probe inputs without the grounds!
My excuse is I've been really sick for the last week.
While the theories about SMPS, mobile phones and increased mains EMI in general are attractive, I just don't buy it. That the mains of 30 years ago was cleaner and more predictable in frequency than it is today doesn't sound that likely. 30 years ago, most of Europe still had a large manufacturing industry with lots of heavy machinery creating interference which was certainly magnitudes larger than what we see today. The Solartron's are also very well shielded boxes with conductive linings on the panels inside with will soak up most RFI sources, just as they are intended to do. Also, if this was the case, then how is it that tggzzz's meter is so quiet? Or, for that matter, my 20 year old 34401A? Nah, I don't buy those theories.
I certainly accept that the last digit on any meter, regardless of counts, is generally a random number generator, but the second to last should be stable to +/- 1 count.
It's interesting to note that in the 7061 manual, one can find the following statement:
DRIFT CORRECTION
The instrument automatically compensates for internal drift every
15 minutes but does not interrupt a GPIB input or a keyboard trigger.
Under remote control, drift correction may be turned on and off.
For example, in tracking measurements lasting longer than 15 minutes,
drift should be turned off for continuity of results.
It's interesting that they suggest turning off drift correction on longer measurements. That's all they say about it, so I'm not sure what I should really make of that.
I think I may have to accept that the 7061 is no 3458A and keeping hoping that I'll see one pass by me at the right price some day!
Anyway, I'll get some appropriate logs and see what looking at the Allen plots might reveal. I'll also connect up my Time current source to the rear terminals and have a quick look at how stable mine is on current readings. Plots to follow!