m k wrote: > Hi Warren, > That does seem a very simple way to get the diode at a steady temp, > but then you need to keep the rest steady to stop all the other > uncertainties swamping the nice steady diode you have just created. ****************** One solution that can be used to eliminate ALL the other uncertainties and errors of ALL the other places when building a 10 volt reference standard is by using a "Manual A-Cal" method, as described in the "Sub PPM 10V transfer standard" posting. http://www.febo.com/pipermail/volt-nuts/2011-September/001029.html The way it works is the same basic way that the automatic "A-Cal" feature in the 3458A works. All other voltage errors are eliminated by referencing back to the reference diode's voltage. BTW to keep the mini-Oven really simple, The temperature can be controlled manually without a temperature controller. The diode's temperature can be manual set by just adjusting the voltage across the 1/4 W heating resistor while measuring the thermistor's resistance on a 3 digit ohm meter. The temperature is quick and easy to set manually, in part because of the quick 30 sec TC response time of such a small oven. It is easy enough to manually set the temperature to within 0.25 deg C, which causes well under 0.01 PPM change in the zener's voltage. Too much Fun ws