Note that in the values printed in the frame on the right, the number stays the same, then jumps by an increment that is much greater than one digit. On a PC, this will be 50 milliseconds about half the time and 60 milliseconds about half the time - or 16 and 17 on a Mac. (On a PC running something other than Microsoft Windows 3.11/95/98, you might see something much different. E.g., the resolution is much better on the superior Linux operating system.)
How long the value stays the same suggests the speed of your computer - the one running your browser, not the server. A faster machine will loop more times before the timer value increments.
Click here to see the results of a similar loop in Java.