Returns the frequency (in Hertz) of the specified desktop. The primary desktop always has the index 0.
ExamineDesktops() has to be called before this function to retrieves the informations about the desktops.
If 'Result' returns 0, then the default hardware frequency is used (the user didn't change it).
f = DesktopFrequency(0)
If f = 0
MessageRequester("Display Information", "There isn't set any desktop frequency, the standard hardware frequency is used.")
MessageRequester("Display Information", "Frequency of desktop: "+Str(f)+" Hz.")