Remeber that web application are stateless. webform_1 won't be able to remember previous values. You need to save the values. There are many ways of saving the values. The nature and type of the state you want to save will have some infunce as to which mechanism to use. In no particualr order here are some of them.
1.
Session State [
^]
2.
Application[
^]
3.
Cache[
^]
4. Database
5.
Cookie[
^]
If it is simple you may use session variable
Session["MyValue"] = value;
value = Session["MyValue"];
You can pass it to your page as
Query String[
^] as well.