Start from a cold oven and use the manufacturer’s recommended preheat indication, mode and rack position. If you use an oven-safe thermometer, place it where the food normally sits and observe several heating cycles rather than treating one momentary reading as the control temperature. Record set point, mode, rack, cookware, preheat completion, reading times and whether the error is consistently high, low or uneven. Do not touch or move a hot thermometer until the oven and tool are safe to handle.
Repeat once with the same setup. A stable offset across repeated tests is different from wide swings, one burned edge or a slow preheat. Convection mode, dark pans, crowded racks and opening the door can change cooking results without proving a failed sensor. Use the cooking pattern plus readings to decide whether user calibration in the exact model manual is relevant.