private void UncheckHeaderCheckbox(ObjectListView olv, OLVColumn col)
 {
     // unbind event temporarily and uncheck header box
     olv.HeaderCheckBoxChanging -= ObjectListView_DeviceList_HeaderCheckBoxChanging;
     olv.UncheckHeaderCheckBox(col);
     olv.HeaderCheckBoxChanging += ObjectListView_DeviceList_HeaderCheckBoxChanging;
 }