Detect frame rate of flash movie at runtime?

Hello-

Does anyone know how to trace out the frame rate that a swf is currently playing at?
I’ve tried creating two date objects on adjacent frames, running the getTime() method on each and subtracting the difference but it seems to be the same regardless of what I set the movie’s frame rate to in the property inspector…

I am basically trying to monitor the performance of an animation at runtime and make adjustments on the fly based on how fast or slow the movie is playing.

thanks in advance-
stephen