Data loggers from Campbell Scientific are being used for measurement and control as part of a branch bag system at the University Paris Sud-Orsay in France. The data loggers control large polypropylene bags so that they close around the branches of a tree for three minutes during a half hour period. Every 20 seconds during this closure air temperature, CO2 concentration, relative humidity, and photosynthetically active radiation are recorded. Between measurements, the bags are ventilated. The fully automatic system provides net photosynthesis and transpiration measurements by day, as well as respiration data by night. Around 6,500 data points are recorded every 24 hours, enabling the logger to work uninterrupted for more than six weeks if necessary.