There's a solution to the mercury battery issue.
My 35 year-old Canon
35mm SLR camera requires PX625 mercury cells. Today, since they're
Indeed. this is a well-known problem for owners of many older cameras,
and other measuring instruments which depend on the stable voltage from a
mercury cell. Even some older electronic multimeters and more
particularly analogue plotters /recorders used a mercury cell as a
 I suspect some of the old analogue X-Y flatbeds were used on digital
computers. They were certainly used on analogue computers. There, this
sort-of scrapes being on-topic ;-)
Incidentally, I read somewhere that the Eastern Bloc couldn't make
reliable mercury cells at one time, so they designed their cameras not to
need them. Things like Prakticas and Exaktas use a balanced  weatstone
bridge circuit (meaning it's in balance at the correct exposure point)
which is independant of the battery voltage, of course.
 Unlike the Pentax Spotmatic where the correct exposure point is
slightly off-balance (the service manual gives a certain current to be
flowing through the galvaometer coil to get it to the 0 marker). %deity
knows why it was done this way....
illegal in the US from what I understand, there exists
the 'Wein cell'. 1.35V zinc-air battery.
Yes. The problem with zinc air cells is that they have a fairly short
life once you've let the air in. Fune if you're using the instruemtn
every day, not so good if you want to use it for a few days and then put
it away for a few nonths.
There are other solutions too. One is to use a silver oxide cell (again
stable voltage, but not the same voltage as a mercury cell) and drop the
excess 0.2V with a shottky diode. Another is to use a micropower
Of course I don't know exactly what the PC-1211
requires, but it's a thought.
They're not PX625-size, that's for sure... I forget what they are.
Anyway, with 4 cells, a Si diode drops about the right voltage to use
alkaline cells. The unit doesn't depend on the exact battery voltage
(not like a measuring instrument), it just doesn't like 6V. And there's
plenty of room inside to fit a 1N4148 or whatever.