The following example demonstrates using the TLargeInteger type to query the performance counter. Note that the TLargeInteger type (64 bit integer) can be converted and referenced as a whole by casting it to a Comp type.

Example:
procedure TForm .Button Click(Sender: TObject);
var
  li : TLARGEINTEGER;
begin
  QueryPerformanceFrequency(li);
  ShowMessage(FloatToStr(Comp(li)));
  QueryPerformanceCounter(li);
  ShowMessage(FloatToStr(Comp(li)));
  QueryPerformanceCounter(li);
  ShowMessage(FloatToStr(Comp(li)));
end;