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Thermometer (oven) by AcuRite
This one is accurate and is very easy to read. Over time, ovens can become either too slow or get overly hot so, when wanting to check, hook the thermometer onto the oven rack while preheating and keep it there throughout the time your food is in the oven. (If you keep a pizza stone in the oven, place the thermometer on top of the stone but, of course, remove it before inserting food onto the stone.) If needed, adjust the heat (up or down) according to what the thermometer registers, but it's best to then call a repair service and try to have the thermostat adjusted. This issue usually gets worse, not better, if not addressed.