> 1.4 V *mercury* cell reference You got your things slightly mixed here imho. The reference you should not upside down is a Weston cell, and gives 1.0xxx volts at 20C (not 25C). Mercury cells are indeed used in some older bridge instruments as reference and their working position is indifferent. They look exactly like a button cell (in fact, they are button cells). The most common use is in older cameras (light meter). They have also become unobtainable since greenies have decreed that mercury (which is mined from the earth as is and purified for industrial use) is bad for the earth (they were talking about *their* earth apparently). Of course mercury is toxic, if you eat it, or drink it. Bad stuff. So is too much salt by the way . Peter -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu