Dwyer Instruments - 1211 Handy Roll-Up Manometer are as accurate as the finest laboratory "U" gages/gauges - yet they are made to roll up compactly for easy carrying and to withstand rough usage. Simply unroll the Slack Tube Manometer and set up to read static pressure, vacuum, or differential pressure. Magnetic clips hold it firmly to any steel surface or hang it on a nail. Turn connectors one revolution to open. When the pressure is imposed, add the number of inches one column travels up to the number of inches the other column travels down. When reading is completed turn connectors to seal columns, roll up manometer into compact coil and tuck it away in its circular metal case or a tool box. No fluid lost. No loose caps or inserts to lose. Dwyer Slack Tube Manometers cover a wide range of pressure readings - from 4-0-4 inches up to 60-0-60 inches. Use them in determining velocity and static pressures, for leakage, fan and blower tests, calibrating control devices, checking gas pressure and many other applications. All models have flexible vinyl-plastic columns and flexible spring steel scale calibrated in inches of water using water; and inches of mercury using mercury. Scale is center-mounted between columns to eliminate parallax error and has a full 2" sliding zero adjustment. All Dwyer Slack Tube Manometers feature exclusive molded nylon tubing connector assemblies with rapid shutoff design in an acrylic plastic top. One turn counter clockwise and the instrument is ready for use. Another turn seals the tubes completely. Molded all-nylon construction makes this assembly corrosion-proof, leakproof and practically unbreakable. Tubing connectors extend horizontally allowing 360° freedom. Tubes won't bend or pinch off. All models have over pressure safety traps in the top of both columns to prevent loss of fluid due to over range pressures or surges in pressure. Slack Tube Manometers are suitable for intermittent total pressure to 50 psi and vacuum not exceeding 20" Hg. Avoid temperatures above 130 deg Fahrenheit and continuous high total pressure. Not for use with red gage oil; use only water or mercury.