One Year Drift Plot

[wn1fju]

Here's the result of a one year measurement of typical drifts one might expect in a basic home setup.  Before you guys get upset, I fully
understand that this is NOT metrology-grade. 

I took monthly readings of a Malone VREF10-003 (30 ppm) 10V reference against an HP 3456 6-1/2 digit and Advantest R6871E 7-1/2 digit
DMM.  The equipment was left off except for a two-hour warmup once a month when I made the measurement.  The measurements were
done by averaging the results of 5 pairs of readings, each pair yielded (x - y)/2 where x = leads in normal position, and y = leads reversed.  The
same test leads were used throughout.

The graph shows the ppm error off of the nominal 10V along with the approximate temperature in the lab.  The temperature was offset by
60 degrees so it would plot on the same axes (i.e, a plotted value of 4 means 60+4 = 64 deg F).

Of course, since the Malone reference could be drifting in addition to the two DMMs, it's hard to reach a definitive conclusion.  But, feel free to
weigh in with your conclusions (other than I need to get a calibrated 1 ppm-class reference)!

[Kleinstein]

There seem to be quite some correlation fo the temperature and the difference between the two meters. So at least one of the meters seem to show quite some TC.

Hard to seen much more from those data.
To see more it might help to have data over a slightly larger temperature range. This way one could get a correlation coefficient or curve and correct the rest of the data accordingly.

Just turning on the DMM for a few hours is not long enough to establish a stable humidity level. So it is not a surprise the 2 meters behave slightly different. The high grade meters are usually made to run 168 hours a weak. There can be a few 10 ppm of drift for the first day or so you turn the meter on after a month of storage.