Usage of doPostBack in a real environment

input type="text" name="t1" id="Tx1" onserverchange="Text1_ServerChange" runat="server" onblur="enablePostBack();"

input type="text" name="t2" id="Tx2" runat="server"

//script for postbacking
script language="javascript"
function enablePostBack()
{
//T1 is the first argument(name of our control) I mentioned earlier and give the
// value of second argument as "" that's all
__doPostBack("Tx1","");
}
/script

//c# functon

protected void Text1_ServerChange(object sender, EventArgs e)
{
Tx2.Value = (Int16.Parse(Tx1.Value) * 45).ToString();
}