Ditto on the oven thermo meter, the dial on the stove will have a set screw on the back or something, to make an adjustment so the dial setting comports with the actual temperature.
With experience, one can tell just by looking at a piece of meat when it’s done. Slow cooking on a spit over coals outdoors even. But they are useful to gain that experience, undercooked is easily repaired, overcooked is not and makes a big difference. For large hunks of meat, why not?