"Dick Adams" > wrote in message
...

"Mike Avery" > wrote in message
news:mailman.7.1176482550.1838.rec.food.sourdough@ mail.otherwhen.com...

> Oven thermostats, to be kind, suck rocks. Most are off by considerable
> amounts, and many vary.

The kind I have in my old Kenmore gas range is very reliable, and quite
accurate, and, if not, is adjustable, though it has been difficult to find
out
how it works and how it is adjusted. Furthermore, it has required, at
rather
long intervals, to be disassembled for the purpose of cleaning its set of
electrical contacts. I found out by asking questions at r.f.s. that it,
generically,
is a "millivolt control" which means it relies on current generated by a
pilot-flame-heated thermocouple to actuate the solenoid that opens the
gas valve when a heating cycle is called for. The regulation is quite fast,
with the on-off cycles lasting about 10 seconds at bread-baking
temperatures,
and so precise that the fluctuation could not be noticed with a conventional
oven thermometer (though amounting to several Fahrenheit degrees when
recorded with a thermocouple thermometer). There is no doubt that the
recorded temperature depends on where in the oven the temperature sensor
is placed.

The opinion of the repair man is that the stove is too old and should be
replaced. I think it was made in the 1950's. It is quite likely that the
elements
of the thermostat could not be replaced. For one thing, the thermal sensor
is
probably based on the expansion of liquid mercury, which is abhorred by
the protectors of the environment (who, incidentally, do not know shit
about protecting against carbon and military).

So it goes!

--
Dicky

Just how is an oven thermometer tested for accuracy and repeatability and if
it's off how is it calibrated ?

Bill