[volt-nuts] How long can standard cells last?

[ed breya]

I just junked out a very beat up old Fluke 803 differential 
voltmeter, and found deep within, an old-school Cd/Hg standard cell. 
It was well protected in an aluminum box, and wrapped in foam and 
foil. It looks brand-new, and still measures around 1.018... V. I'd 
like to keep this one as another reference point if it's still good. 
I assume that it just wasn't used much, or that the Fluke circuits 
were very good at not loading it down.

I'm sure it is the original unit installed in the instrument - marked 
5/12/1960. It is a Muirhead D-845-C. There's no test voltage tag or 
any other info but a serial number.

So, I'm wondering if a 52 year old standard cell can still be OK, and 
if anyone knows the specs on these, or where to find the info. I 
don't know if it's possible, but I'd like to find what the official 
voltage was supposed to be to a few more digits resolution. I think 
various types and brands each had slightly different nominal voltages 
around that determined by the basic chemistry. I remember in the old 
days, every one I saw included a sticker with the 25 deg C exact 
voltage measured as accurately as possible back then against the NBS. 
I'd like to especially know if this is a saturated or unsaturated cell type.

Ed