I don't understand this expression in one of the example calculating queue-delay. set delay [expr 8 * [$bytesinteg set sum_] / [[$link link] set bandwidth_]] Regards, Arun -- Arun Gandhi M.S. (Computer Science) Phone : 603-862-7614 (Res) University of New Hampshire, 603-862-3786 (Off) Durham, NH 03824 Email : [email protected]