I have a 7081, and it has been remarkably stable. I have two Datron 4910 voltage standards, calibrated by Fluke at an outrageous cost. I compare the 7081 to them both regularly. I've found that I rarely have to recalibrate (maybe once every year) to maintain 1ppm on the 10V range. It's quite amazing. BTW, the reference in the 7081 isn't an LTZ1000, or even an ovenized reference. It's just a plain old 1N849A with a tc of 5ppm/degC worst-case. Solartron then biases it via a DAC to the current that gives minimum tc (factory calibration), and then adds a temperature-dependent 2nd-order compensation voltage to the result. Brilliant bit of engineering. And yes, aging is a wonderful thing. >Gbusg wrote: >Again, I don't have personal experience with it, but my thinking is that, of >the instruments you've collected, your Solartron 7081 might actually be the >most stable at 10Vdc. Certainly it has the tightest spec: 4.3 ppm 2nd year >after calibration. Given the probable age of your 7081, I can imagine that >its 10Vdc aging might indeed have slowed way down (to a very desirable slow creep)? -- Bill Ezell ---------- They said 'Windows or better' so I used Linux.