[uzgrzkla] Countdown

Cheap digital wristwatches usually have alarms and stopwatches but rarely countdown timers.

To time how long it takes to do something, but for which one may be too distracted at the end to stop a stopwatch or note the time, set a countdown timer with the estimated time at the beginning.  The accurate interval time may be found by bisection, updating the estimated time each iteration.  This takes many trials.