{
TStopwatch from about.delphi.com, author as far as I know is Zarko Gajic.

Here's an example of usage:

    var
      sw : TStopWatch;
      elapsedMiliseconds : cardinal;
    begin
      sw := TStopWatch.Create() ;
      try
        sw.Start;
        //TimeOutThisFunction()
        sw.Stop;

        elapsedMiliseconds := sw.ElapsedMiliseconds;
      finally
        sw.Free;
      end;
    end;

}
unit StopWatch;

    interface

    uses Windows, SysUtils, DateUtils;

    type TStopWatch = class
      private
        fFrequency : TLargeInteger;
        fIsRunning: boolean;
        fIsHighResolution: boolean;
        fStartCount, fStopCount : TLargeInteger;
        procedure SetTickStamp(var lInt : TLargeInteger) ;
        function GetElapsedTicks: TLargeInteger;
        function GetElapsedMiliseconds: TLargeInteger;
        function GetElapsed: string;
      public
        constructor Create(const startOnCreate : boolean = false) ;
        procedure Start;
        procedure Stop;
        property IsHighResolution : boolean read fIsHighResolution;
        property ElapsedTicks : TLargeInteger read GetElapsedTicks;
        property ElapsedMiliseconds : TLargeInteger read GetElapsedMiliseconds;
        property Elapsed : string read GetElapsed;
        property IsRunning : boolean read fIsRunning;
      end;

    implementation

    constructor TStopWatch.Create(const startOnCreate : boolean = false) ;
    begin
      inherited Create;

      fIsRunning := false;

      fIsHighResolution := QueryPerformanceFrequency(fFrequency) ;
      if NOT fIsHighResolution then fFrequency := MSecsPerSec;

      if startOnCreate then Start;
    end;

    function TStopWatch.GetElapsedTicks: TLargeInteger;
    begin
      result := fStopCount - fStartCount;
    end;

    procedure TStopWatch.SetTickStamp(var lInt : TLargeInteger) ;
    begin
      if fIsHighResolution then
        QueryPerformanceCounter(lInt)
      else
        lInt := MilliSecondOf(Now) ;
    end;

    function TStopWatch.GetElapsed: string;
    var
      dt : TDateTime;
    begin
      dt := ElapsedMiliseconds / MSecsPerSec / SecsPerDay;
      result := Format('%d days, %s', [Trunc(dt), FormatDateTime('hh:nn:ss.z', Frac(dt))]) ;
    end;

    function TStopWatch.GetElapsedMiliseconds: TLargeInteger;
    begin
      result := (MSecsPerSec * (fStopCount - fStartCount)) div fFrequency;
    end;

    procedure TStopWatch.Start;
    begin
      SetTickStamp(fStartCount) ;
      fIsRunning := true;
    end;

    procedure TStopWatch.Stop;
    begin
      SetTickStamp(fStopCount) ;
      fIsRunning := false;
    end;

end.