The Fieldpiece Superheat amp; Subcooling for Air Conditioning & Refrigeration meter, model SSX34, measures suction line, or low side, line temperature and pressure. It then calculates actual superheat in real time using built-in P/T charts. It also measures liquid line, or high side, line temperature and pressure, and calculates actual subcooling. Use it to get actual superheat on R-22, R-410A, R-134A, and R-404A fixed orifice systems and actual subcooling on TXV / TEV regulated systems. Use the "T" fitting to charge to actual superheat or subcooling by putting the SSX34 in-line between your refrigerant bottle and the system.