how do i use the pll block of simulink to measure frequency?

Hi, I am trying to use the pll block of simulink to measure the frequency of a variable frequency system but the block always gives me just the value I input as the initial frequency. How can I Use this block to measure a frequency which may/may not have anything to do with the initial frequency? Is there any other way I can measure frequency on simulink?

[rucha joshi]

i am facing the same problem.is there any solution???