The Testo 550 is a high-performance Refrigeration System Analyzer that accurately performs temperature and pressure measurements in seconds. It automatically calculates superheat and subcooling for 31 different refrigerants, quickly and easily. With a large easy-to-read back-lit display and two temperature inputs, it can calculate superheat and subcooling simultaneously in real-time. The 550 is simple enough to use right out of the box and rugged enough for daily use by today's demanding HVAC technicians.