Soft boiled egg timer
Six minutes in already-boiling water gives a set white and a properly runny yolk, starting from a fridge-cold large egg.
The useful range is narrow. Five minutes leaves some of the white loose near the yolk. Seven gives you a jammy centre. Nine and it is hard boiled. A minute is the difference between three quite distinct eggs, which is the whole reason to time it rather than guess.
Lower the eggs in on a spoon rather than dropping them, and move them to cold water the moment the timer goes. Carry-over heat keeps cooking the yolk otherwise.
Or set any length you like: gotimer.app