what is Timescale ?

From tutorial 4:

The movie's timescale is the timing resolution of the movie per second. Dividing the duration of a movie by its timescale will tell you the approximate length of the movie, in seconds. Our crashtest.mov file, for example, has a duration of 2836 time units and a timescale of 600. The movie should run for about 4.73 seconds. If we want to move two seconds into the movie, we could set the jit.qt.movie object the messagetime 1200 (1200 time units divided by a timescale of 600 units/second gives us 2 seconds).

The fps, or frames per second, of a movie tells us how many individual video images exist in the movie every second. The higher the fps of a movie, the smoother the apparent motion of the movie will be (assuming, that is, that the individual frames are all in some way unique). Some common fps rates are 15, 24, 29.97, and 30. Our movie file in this example runs at 15 frames per second, which works out to a new frame of video every 40 time units, or about every 66.7 milliseconds. If we divide the duration of crashtest.mov by the number of time units per frame in the movie, we can determine that the movie file has 70 frames. If we wanted to, we could get the total number of frames in the movie by querying the jit.qt.movie object with the getframecount message, but then we wouldn't get to do the fun math!