I saw this cheap easy way to see if your oven is hotter or cooler than it's supposed to be.

Make 2 small trays from aluminum foil.  Put a tablespoon of sugar in each.

Set oven to 350°, let the oven attain that temperature.  Place one tray in the oven, take out after 15 minutes.

Now set oven to 375°, let oven attain that temperature.  Place the second tray in the oven and take out after 15 minutes.

If the first is still white sugar and the second is brown oven is accurate enough.

If both are still white, oven is too cool, if both are brown oven is too hot.

Sugar caramelizes  at 367°.