Access variable from one form to another

[question]

Person1 First Form
--------------------
Private
FOldID:Integer
procedure SetOldID(Value: Integer);

public
property OldID: integer read FOldID write SetOldID;
..
..
..
procedure TPerson1.SetOldID(Value: Integer);
begin
FOldID := Value;
end;

procedure TPerson1.ADD(OldID: Integer);
begin
OldID = OldID+s:
end;
----------------------
Second Form called Person2

Now i want to use the value (OldID) from TPerson1.ADD(OldID: Integer) in Person2 Form,in following situation
..
..
..
z: Tperson1

if bool = True then
z.Add(z.OldID)


i have tried with property but it does not work ,could you please give me suggestion ?