Perhaps somebody may be interested in little stability study of above-mentioned 5700A.
Unit was calibrated in beginning of the year, against SR104 and Fluke 732B (both in <6 months from subppm standards lab cal).
Since that time we run calcheck's on various periods, storing all data. Lab temperatures were kept around 24-26°C. Unit was mostly 24/7 online till summer time.
Last few months it was turned off, and powered on just couple days ago before 8/29 calcheck.
Here's snapshot on resistance function:
I'd say not too shabby at all for 26-year old calibrator. Ohm board was replaced at some point with one made in 2005, according to IC datecodes.
Here's how it look like, in case you forget:
Given that lab was not controlled very well, no humidity control, I'd say numbers are very nice, well under 3ppm for all resistances except 100Meg.
Major 1K, 10K, 100K resistors are better than 1ppm stable over this 8 months period.