[NumLock]

Код:

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    procedure FormCreate(Sender: TObject);
    procedure EditsChange(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure EditsChange(Sender: TEdit);
begin
  Sender.Text:='--';
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  // вот это можно и в цикле сделать
  // если TEdit вообще сильно много
  Edit1.OnChange:=EditsChange;
  Edit2.OnChange:=EditsChange;
end;

procedure TForm1.EditsChange(Sender: TObject);
begin
  Unit1.EditsChange(TEdit(Sender));
end;

end.