That is dependent on the operating system's time-reporting function. My memory is that UNIX systems will provide a more precise resolution (or a finer "granularity") than Windows for its systime() output, I think, however, that Windows ***IS*** providing millisecond granularity. Here is the output from my IDL For Windows XP just now: IDL> print, systime(/SECONDS), FORMAT='(D30.12)' 1198128200.096999900000 IDL> print, systime(/SECONDS), FORMAT='(D30.12)' 1198128203.065000100000 IDL> print, systime(/SECONDS), FORMAT='(D30.12)' 1198128204.954999900000 IDL> print, systime(/SECONDS), FORMAT='(D30.12)' 1198128209.829000000000 IDL> print, systime(/SECONDS), FORMAT='(D30.12)' 1198128223.763999900000 IDL> print, systime(/SECONDS), FORMAT='(D30.12)' 1198128227.293999900000 IDL> print, systime(/SECONDS), FORMAT='(D30.12)' 1198128230.216000100000 IDL> print, systime(/SECONDS), FORMAT='(D30.12)' 1198128233.480999900000 If you consider the '999's to be equivalent to '000's (carry the 1), I believe that the above output is demonstrating millisecond granularity. Are you seeing something different and lesser on your machine? James Jones ITT Technical Support