Anti-flutter gauges smooth out needle movement Professional extruded aluminum block Easy to read temperature / Pressure scales on 3-1/2 gauge face (Bar/Psi/°F /°C) Free-floating piston type valves reduce o-ring wear Large easy-to-grip front-facing knobs Extra large sight glass for visual check of refrigerant. Extra access port for vacuum line1. Close both valves on the manifold gauge set by turning the high and low knobs clockwise. 2. The gauges are correctly calibrated at the factory before shipment. If calibration is required, insert a straight blade screwdriver into the adjusting screw on the gauge face. 3. Attach the high and low couplers to the male end of the red and blue hoses. If using manual couplers, open the plunger by turning the knob counter-clockwise prior to connection to the system. If quick couplers are used, pull the sleeves up to unlock position before attaching to an A/C system. NOTE: Attach 12 mm-m x 14 mm-f R1234yf adapters to R1234yf couplers before connecting to the red and blue hose. 4. Connect the red hose to the high side port and the blue hose to the low side port on the manifold gauge.