Actually the densitometer is a device for scanning gels and films and outputs the data to a strip chart recorder which makes graphs out of it. The data is a voltage data from 0 to 1 volt. Now Hoefer also makes a data logger interface whcih can be connected to the densitometer instead of the chart recorder and the data logger is then connected to the computer through a serial port. The software is necessary to collate and interpret this data and then caluclate area under curves and so on.