Large professional-size (16 1/4") tester is accurate at all temperatures . Tests coolant, hot or cold . Easy to read discs are magnified by convex design of the clear SAN plastic barrel . Protection scale is printed in both Celsius and Fahrenheit. Beyond 70% anti-freeze, cooling and corrosion effectiveness is reduced. One-piece bulb and neoprene dip tub This large professional-size tester is accurate at all temperatures and is used to test coolant, hot or cold. It has a special feature, the 6th disc shows overprotection and a loss of cooling efficiency. Made with the durability to last!