This tool records data over time or in relation to location via instruments and sensors that can measure the parameters of interest. There are sensors that measure just about anything—temperature, humidity, voltage, current, air velocity, CO, and so on. Hook the sensors up to a data logger that records the sensor measurements over a period of time. Download those data into a computer and analyze the logged data to solve, or define, a problem.
See: Steve Mann, “Data Logging Primer”
Home Energy, 27.5, July/Aug, 2010