My oven always took longer to bake things than recipes said, so I bought an oven thermometer to check it, and sure enough it underheats by a lot. So I pulled out the instructions to calibrate it, and the instructions say that store-bought oven thermometers aren’t reliable! So basically my oven says the thermometer is a lying liar, and the thermometer says my oven is a defensive liar. Who should I believe???