From my understanding, the GSR sensor is actually measuring the change in skin resistance and outputting this as a voltage level (0-5V for Arduino Uno) and is not directly measuring the skin conductance (this would require a constant voltage and a measurement of current between the electrodes which the ADC on the Arduino does not measure). Thus, with greater levels of human arousal, the resistance will decrease and therefore voltage should increase. However, from looking at the output graphs on the wiki page it seems that voltage is proportional to the resistance - it decreases with greater arousal which goes against my initial thoughts of voltage being inversely proportional to resistance.
Therefore, please could someone clarify what the output of the GSR actually represents and the what the sensing circuit is measuring (e.g. resistance or conductance) and how it is achieving this. Your feedback on this matter will be much appreciated. Thanks.