This time of year we get many calls to calibrate an ovens temperature. In most cases, you can do this yourself. We recommend using two of the small round oven thermometers https://amzn.to/33QPXTB. Most ovens have a calibration mode that lets you adjust the temperature up or down by up to 35 degrees. Place the oven thermometers on the middle shelf and turn the oven to the temperature you prefer to cook at, typically 350 to 400°F. Give the oven 30 minutes to an hour for the most accurate results. Check the temperatures on the oven thermometers. Hopefully they are the same… If the temp is off by 30 degrees or less, it can be calibrated. If it’s off more than that, you need service. Your user manual should have instructions on calibration. If you don’t have the user manual, most are available online at the manufacturer’s website.