Passing control values - some suggestions

In form 2, create the method you want to pass data into:

public void stuff(double val)
{
MessageBox.Show(val.ToString()); //whatever processing you want here
}

The key here is the "public" keyword at the start of the function declaration. This means methods in other classes (that is, classes outside the form, can call the function.

in some method on form 1 (like a button for example):

Form2 frm2=new Form2(); //create the new form
frm2.stuff(1.7); //call the function on form 2. replace the 1.7 with whatever double variable