You cannot be a consistent baker without one of these!
Most ovens do not register correctly--even new ovens. They can't. They heat up until they get above the setting, turn off,and start to cool. When it drops below the setting, it turns on again. It's constantly turning on and off on a timer.
Stick an oven thermometer in your oven. Just clip it to a rack--it'll hang out of the way--and leave it there.
When you go to put something in the oven, glance at the thermometer to see if it’s where it is supposed to be.
Now that you know how your oven bakes, get a thermometer and be a better baker!