Tappan Oven #MEF500PBWD heating unevenly

Perhaps the item you are using to check temperatures is not accurate. I my line of work, I use a digital thermometer which records immediate temperature. Perhaps understanding the process will help you see more accuracy in the way you read the temperature in your oven. Allow me to offer this explanation....First of all, place your thermometer near on the top rack as close to the oven temperature probe as possible. This probe is the focal point for your oven and detects the temperature and opens the electrical circuit to turn off the element when the desired set temperature is attained. Set your electric oven to 300 degrees and hopefully, you have a window in your oven to watch. The bake element will come on and the temperature will rise until it reaches 300 degrees. It is at this point when your oven bake indicator light should go out. When this happens....look inside. The element is still bright orange and emitting heat and will continue to raise the temperature in the oven to approximately 325 - 340 degrees. With this noted, you will see the temperature beginning to drop 315, 310, 300, 295, 290, 285 perhaps even 280 or some even lower to 275 and then the indicator lamp will go on indicating the circuit has closed thus turning on the element, Finally there is a variance and no range GAS or ELECTRIC will ever maintain a even 300 degree temperature. The calibration set point is based on the 300 degrees. If your oven light goes off within 20-25 degrees of three hundred degrees, your oven is already calibrated pretty close and I would not attempt to adjust it at all.