bought a used house 1 yr ago. home inspection report indicated upper oven temp was 347 degrees when set to 350 degrees.

We don't use it much but each time I do the upper oven is never as hot as the setting. I bought a oven thermometer and measured it and it's as much as 50 degrees lower than oven setting. It also seems to take forever to heat up to the setting. Whenever the oven beeps and says it is heated up (say 350) it actually is still way under that setting (maybe 260 according to the thermometer).

I adjusted the temperature offsett by adding 35 degrees but still doesn't quite get up to oven setting. I have had to add 10 degrees to the oven temp to get to the desired temps even after adding 35 degrees with the oven offsett. With all of this you have to wait at least 15-20 mins to get the oven up to the desired temp AFTER the oven says it is already there.

don't understand what is going on. Any advise? Can't figure out how home inspector got acceptable readings and I can not. It obviously had some kind of problem but don't know where to start.