Assemble the black rubber,there is a hole on it, mainly for protecting the densimeter from being sucked into the gasbag. 2. Put the densimeter into the glass tube. 3. Assemble the sucking . 4. Then assemble the gasbag. Its main function is for measuring electric battery fluid density. 5. When using, put the meter vertical immerse in a transparent container, then you can read electric liquid density from the table at any time. 100% brand new and high quality. Professional for measuring acidity and alkaline storage battery solution. Professional for measuring acidity and alkaline storage battery solution. Its main function is for measuring electric battery fluid density. When using, put the meter vertical immerse in a transparent container, then you can read electric liquid density from the table at any time. Country of origin : Taiwan