What is a calabrating battery type called?

In my Physics lab, when I taught at a University, we had a single cell battery with an accurately known output voltage. It was a primary cell, and due to the chemistry of it this had a voltage that was known and stable to about 8 decimal places. We used it for calibration as you couldn't take more than a mA or so out of it.

Unfortunately I can't remember what the battery chemistry was called.

Can anyone remember?

Thanks

Standard cell?

http://www.nist.gov/calibrations/voltage.cfm

LarryD:
Standard cell?

Thanks.
Yes that is what it is but it is not the type.

However, asking the question did jog my memory, it is in fact a Weston cell.
Cheers

If memory serves me correctly, (it's over 50 years since) we used to use them on Cambridge Pots/bridges in conjunction with wet ice flasks (cold junction compensation) for the calibration of thermocouple systems.

At that time all our instrument systems were valve operated and, although maybe now considered ancient, were extremely capable of running a nuclear power plant.

Their voltage was somewhere around 1.018 and their output current capability was zero. Woe betide the apprentice who failed to balance the bridge so that no load was placed on the cell

Weston cell. I'd forgotten the name, too.

http://electronicspani.com/standard-cell/

Pretty amazing, Insanely high accuracy 1.01830V @ 20C.