Simply insert any of these compact, 4.5" (11.4 cm) L loggers into your computer USB port, name it, choose your required sampling rate, select high and low alarms if required, and set the logger start time. Once configured, the logger can be removed from the computer to log independently. Data is downloaded back onto the PC where it can be analyzed and viewed as a graph using included software. Use model 23039-58 for a 0 to 1000 ppm range and model 23039-68 for a 0 to 300 ppm measurement range; both store more than 32,000 readings. An bright red LED will flash and an audible alarm will sound when the user-determined level is exceeded.