Uses Windows system timer.
System timer resolution is low than onboard system timer, but unlike
Windows timer, its delay are not accumulated. *1
The accuracy differs from one OS to another.
For example, on Windows XP, the minimum resolution is about 16ms.
The resolution of system you are using is displayed in [System Timer Resolution] item when you issue the diagnosis report from diagnosis program.
*1 Because the timing is based on the measurement begin time, not based on the last notification time.