usleep suspends execution for microsecond intervals.
wait for 1 microsecond:
$ usleep 1
wait for 1000 microseconds, which is 1 milli second:
$ usleep 1000
wait for 1 million microseconds, which is 1 second:
$ usleep 1000000
sleep 1 is equivalent to usleep 1000000
BUGS : Probably not accurate on many machines down to the microsecond. Count on precision only to -4 or maybe -5.
If you have a fast PC like a 2 GHz P4 or AMD, the accuracy is ok.