You cannot be a consistent baker without one of these!
Most ovens do not register correctly--even new ovens. With an oven thermometer you can know at any temperature.
Stick an oven thermometer in your oven. Just clip it to a rack--it'll hang out of the way--and leave it there.
And when you go to put something in the oven, glance at the thermometer to see if it’s where it is supposed to be. Crank the setting up or down if you need to.
Now that you know how your oven bakes, get a thermometer and be a better baker!