Hi, does anyone know how many watt hours it takes for a conventional residential electric oven to go from cold to 500F? (I don't think it's just the wattage of the bake element x time. The resistance of the element changes as it heats up. Besides, the broiler element turns on sporadically help to get up to temperature faster.) I could rig up a cable and use my Kill-A-Watt meter but the cable and plugs required would probably cost me at least $50.