The Myron L Ultrapen PT4 is a groundbreaking, new pocket tester for measuring free chlorine disinfecting power, free chlorine equivalent (FCE), as well as temperature. It is waterproof and designed to be extremely accurate, fast, and simple to use in diverse water quality applications. The FCE function measures the real, unaltered chemistry of source water, including moment-to-moment changes in that chemistry. The PT4 requires pH4, pH7, and pH10 pH Buffer solutions and 80 mV Quinhydrone, 260 mV Quinhydrone, or 470 mV MLC Light's ORP standard solutions for wet calibration, and sensor storage solution for proper storage.