OK reference source for most uses. Better can be bought but this is "not too bad" for the money. Element 1110 $4.89 NZ in ones http://nz.element14.com/analog-devices/adr3430arjz/ic-volt-ref-3v-6sot23/dp= /1843662 http://www.farnell.com/datasheets/608881.pdf 1.2V reference 0.1% as supplied worst case output error Call that 1000 ppm for comparison 8 ppm/C -40 - =3D125 7/50 typ/max ppm with Vin (presumably at 25C or fixed temp) 160 ppm/V Vin max across temp 14/30 ppm / mA sourcing 7/50 ppm / mA sinking Stability 1000 hours 50C =3D 30 ppm SO: Drive from a 3 terminal regulator. Load at constant load. Vaguely oven (eg aircon room). Or for lower power than ovening, use processor or other to calibrate for temperature effects. Should be able to keep under 100 ppm without much effort or 10% of absolute initial spec. So MAY be able to build a device at relatively modest cost which can be assembled untrimmed to 0.01% stability and 0.1% accuracy and trimmed down t= o 0.01% accuracy. Russell --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .