Oven does not maintain a consistent temperature

Is this oven gas or electric? If it is gas then it can be normal to see 30 to 50 degrees difference in tempature. The tempature in a gas oven works on the average tempature. For example: The oven tempature may rise all the way up to 370 degrees. Then the burner will shut off. And then the tempature can drop all the way to 330 degrees. Then take 330 and add that to 370 then divide that number by two and the average tempature will be 350. If your oven is electric then the tempature should be much more consistant but can have a 10 to 15 degree variance. Also the standard oven tempature guage that you put in the oven or even the temp guage built into the oven are not very accurate. We us a Fluke meter with a thermocouple to calibrate an oven. So to check your oven for proper tempature regulation you will first need to let the oven pre-heat for about 15 minutes. Then place the thermocouple in the center of the oven. If the oven is electric the take a temp reading every 5 minutes and average them out. If the oven is gas then you will need to take a temp reading when the tempature reaches it's highest and lowest points. Take at least 5 consectutive readings and average them out. You should get an average within 10 degrees of set temp(350 degrees). If it is off by 35 degrees or less you can usually caluibrate the thermostat back to proper temp. This procedure can be different for each range model. If it is more than 35 degrees off or you are getting irratic readings then the thermostat or thermostat components might need to be replaced.