<graph string="Tasks Analysis" sample="1" disable_linking="1">
                     <field name="project_id"/>
                     <field name="stage_id"/>
                     <field name="nbr" invisible="1"/>
                     <field name="working_hours_open" widget="float_time"/>
                     <field name="working_hours_close" widget="float_time"/>
                     <field name="rating_avg" invisible="1"/>
                 </graph>