Got a new water kettle that has different temp selections for different teas. If you select a less than boiling temp, it’s smart enough to stop heating early, wait for the termometer to catch up, then give another burst of heat to reach the target. Fair enough.

OTOH, if you boil water, it does not bother to stop and read. Perhaps prioritizing speed over energy waste. When the water is bubbling like crazy, it’s clearly boiling at which point the thermometer shows 90°C. So it keeps heating to 100°C. Are thermostats generally that slow and far off? Or is my kettle’s thermometer particularly slow?

Low tech electric kettles which only boil the water have no thermometer AFAICT. Is it steam that triggers the off switch? Would that be faster than a thermometer that is 10° behind?