Stopwatch different timing why?

[skoja07]

I am using a stopwatch start and stop in order to find out the time of process of a web service how ever when I refresh the page in order to do another test using the same parameters, data an all but the second and all the other test bring back different results. But when I restart the IIS server it again shows the initial result.So my question is why do I receive a different result in time the first time?By the way I wrote the web service in C#.