The CL201 is a portable 2-in-1 digital water quality tester for measuring residual chlorine (0.01-4.00 ppm or mg/L) and temperature (0-60°C or 32-140°F). It features an LCD screen with a backlight, a pen-style handheld design with a protective cap, and simple push-button operation, making it ideal for swimming pools, spas, and aquariums.