function g_unitValCallback(hObject, varargin)
   
   global params
   
   currParamIndex = get(hObject,'UserData');
   oldUnit = char(params.params(currParamIndex).val);
   oldUnit = oldUnit(2:end-1);
   newUnit = strrep(get(hObject,'String'),'''','');
   try
      params = pset(params,params.params(currParamIndex).key,unit(newUnit));
      set(hObject,'String',['''',newUnit,'''']);
   catch
      set(hObject,'String',['''',oldUnit,'''']);
      return;
   end
   set(findobj('Tag','apply'),'Enable','on');
   set(findobj('Tag','undo'),'Enable','on');
   
end