Hello

I'm trying change GetTickCount from my codes to QueryPerformanceCounter

code:

Code:
type TCustomTimer = class
  private
    PerfFrequency: Int64;
    InvPerfFrequency: Single;
  public
    function gettime: Single;
    constructor Create;
  end;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    Memo1: TMemo;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }

    procedure Teste(Sender: TObject; var Done: Boolean);
  end;

var
  Form1: TForm1;
  clock: TCustomTimer;
  _start, _end: Double;


implementation

{$R *.dfm}
///////////////
{ TCustomTimer }

procedure TForm1.Teste(Sender: TObject; var Done: Boolean);
begin

   _end := clock.gettime;



   //1000 = frequencia de intervalo em milesegundos


   if (_end-_start) >= 1000 then
   begin

     memo1.Lines.Add('evento');
     _start := _end;


   end;

end;

constructor TCustomTimer.Create;
begin
  QueryPerformanceFrequency(PerfFrequency);
  InvPerfFrequency := 1.0 / PerfFrequency;
end;

function TCustomTimer.gettime: Single;
var
  Time: Int64;
begin
  QueryPerformanceCounter(Time);
  Result := 1000 * InvPerfFrequency * Time;
end;
///////////////

procedure TForm1.FormCreate(Sender: TObject);
begin


  clock := TCustomTimer.Create;

  
  _start := clock.gettime;

  application.OnIdle := Form1.Teste;


end;

procedure TForm1.FormDestroy(Sender: TObject);
begin

  Clock.Free;

end;
my code is ok?


my question...

what is this line?
Code:
 InvPerfFrequency := 1.0 / PerfFrequency;