How to read the CPU utilization values shown in Task Manager

Hi all,

I am trying to monitor the overall CPU utilization and show it in my application(built using LabVIEW). Most of the online search suggests using performance monitor counters but the values are way off (sometimes 30% difference) from what is displayed in Task Manager.

I would like to understand how the Task manager computes CPU usage and is there any DLL or Command line to get that value. 

Thanks,

Mani