device for checking, before start-up and after shut-down, that all or part of the measuring system is either filled completely with liquid (full hose measuring systems) or completely empty of liquid (empty hose measuring system), type of level sensor, a transparent tube through which the operator of a tank or boiler can observe the level of liquid contained within, läbipaistev toru, mille kaudu paagi või katla käitaja saab jälgida selles sisalduva vee taset