-.Fa useconds
-microseconds have elapsed
-or a signal is delivered to the thread whose action
-is to invoke a signal-catching function
-or to terminate the thread or process.
-The actual time slept may be longer, due to system latencies
-and possible limitations in the timer resolution of the hardware.
+.Fa microseconds
+microseconds have elapsed or a signal is delivered to the thread and its
+action is to invoke a signal-catching function or to terminate the
+process.
+System activity or limitations may lengthen the sleep by an indeterminate amount.