When I was still catering and had the big Blodgett oven, I had to have it calibrated every two years to comply with the state regulations for commercial ovens. (It could hold 7 full-size sheet pans so the capacity was much more than regular home ovens.
It was a gas oven (convection - and also had a steam function for baking breads and other things that benefit from steam) and they seem to go out of calibration more rapidly than electric ovens.
Some older electric ovens have a large capacitor or a fuse that can gradually go "off" and may need to be replaced. A friend who recently renovated a house built in the 1950s wanted to keep the two ovens (side by side) as they fit the style of the home. One worked okay but the controls had to be recalibrated. The other did not work at all and the problem was the capacitor - the part cost less than 20 dollars and after calibration it worked fine too.
Technicians today have nifty testing equipment so they can isolate a problem quickly without having to take the whole thing apart, as would happen in the old days.
I found
with some helpful information