Forms Data Controls :: Access A Servercontrol (checkbox ) From Jscript And Check If It Was Selected?

I have a gridview that contains check box in first column for each row. I also have a check box outside the grid view called >>>>

<asp:CheckBox ID="chkSelectAll" runat="server" Text="Select All" AutoPostBack="true"
OnCheckedChanged="chkSelectAll_CheckedChanged" />

I either can select more than one checkboxes from gridview then click on a button to get the number of checkboxes selected OR I click on SelectAll checkbox ( which is outside the gridview ) which check all the checkboxes in the gridview and give me the number of checkedboxes. When I select inidividual checkboxes inside the gridview, th e count of number of checkboxes is correct ( displayed in a lable ) However;

When I click "SelectAll" check box, it give me total of all checkboxes chekced in the
gridview + 1 ( extra ) I am trying to get rid of this extra one by checking if this "Allcheckbox" is selected to so I subtract one from the total count .. like this

// java code ... code not shown does capture the total count into c variable
varAllChecked = document.getElementById('chkSelectAll');
if (varAllChecked.checked== true)
litCount.innerText = c - 1;
else
litCount.innerText = c;