Access variable from one form to another

[question]

Hi,
How can pass the same variable in another form, for example, i have two forms, Form1 and Form2


TForm1.Calculation(OldID: Integer)

OldID := 1+1;

now i want to call the value of OldID from Form2. for example

TForm2.btnClick(Sender:Tobject)

Calculation();---> here how can i get the value of OldID from Form1?


if i declare again OldID in Form2 then it shows the value 0