Как изменить системное время?

Code:

procedure TfmTime.btnTimeClick(Sender: TObject);

var

vsys: _SYSTEMTIME;

vYear, vMonth, vDay, vHour, vMin, vSec, vMm: Word;

begin

DecodeDate( Trunc(dtpDate.Date), vYear, vMonth, vDay );

DecodeTime( dtpTime.Time, vHour, vMin, vSec, vMm );

vMm := 0;

vsys.wYear := vYear;

vsys.wMonth := vMonth;

vsys.wDay := vDay;

vsys.wHour := ( vHour - 2 );

vsys.wMinute := vMin;

vsys.wSecond := vSec;

vsys.wMilliseconds := vMm;

vsys.wDayOfWeek := DayOfWeek( Trunc(dtpDate.Date) );

SetSystemTime( vsys );

end;