ASP.NET - want to retrive the value from popup window to parent window

hi am having this coding parent window

<a href="#" onclick="Popup=window.open('TAXLOV.aspx?ITTNO=<%#Eval("ITTNO")%>&SUPNO=<%#Eval("SUPID")%>&MATCD=<%#Eval("MATID")%>&STRCODE=<%#Eval("TAXSTRUCTURE")%>&LUMPSUM=<%#Eval("BPRLS")%> ','Popup','toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=yes,resizable=no,width=800,height=500,left=20,top=20'); return false;"
                                                                        onmouseout="window.status=' ';return true;" onmouseover="window.status='View Item Details';return true;"> View Tax Details</a>



having this in pop-up window

<asp:Button ID="btnupdatesubmit" runat="server" CssClass="button"
                        onclick="btnupdatesubmit_Click" Text="UPDATE" OnClientClick="frmComparativeStatement.aspx.reload(true)" />


if i click the "View Tax Details"(parent window) link button i ll get pop-up window. in the pop-up window i did some calculations after the calculation i assign the value in a label (wen i click the update button). now i want to pass the label value into parent window while close the pop-up

window.opener will get you a reference to the parent "window" object that opened the pop up window.