My early xmas gift was a Digital Oven tThermometer.

Stainless steel probe, long braided wire leading to
a digital temp displlay/timer.

No more peering inside a dark oven
at some miniscule dial to check that roast temp.

I used this gadget to check my oven temperature,
and was surprised at the results.

I laid the probe on the middle oven shelf,
and set the Oven Dial to 275,

I watched the temp climb to 300 before the element turned off.
then, a slow descent to 265 before the element turned on again.

So the oven isn't one smooth heat source,
but rather a series of spikes from 10 below to 25 over the dial temp.

If you put in a large cold item ( turkey ) the oven would spend
most of its time at 25 degrees over the dial setting.

I don't know if 25 degrees "over" is critical,
but it may explain some of my mystery baking results.

<rj>