Simple Stopwatch

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Diagnostics, StdCtrls;

type
  TfrmSW = class(TForm)
    lblSW: TLabel;
    btnStartStop: TButton;
    btnReset: TButton;
    procedure btnStartStopClick(Sender: TObject);
    procedure btnResetClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  frmSW: TfrmSW;
  sw: TStopWatch;
  SWRunning: boolean;

implementation

{$R *.dfm}

procedure TfrmSW.btnResetClick(Sender: TObject);
begin
  if not SWRunning then lblSW.Caption := '00:00:00.000';
end;

procedure TfrmSW.btnStartStopClick(Sender: TObject);
begin
  SWRunning := not SWRunning;
  if SWRunning then sw := TStopwatch.StartNew;

  while(SWRunning) do
  begin
    lblSW.Caption := FormatDateTime('hh:nn:ss.zzz',sw.ElapsedMilliseconds/MSecsPerDay);

    // Handle any external events
    Application.ProcessMessages;
  end;

  // Set form DoubleBuffered property to True to prevent flickering

end;

end.