Our datasets provide an opportunity to examine data analysis and methodology techniques used in green computing research. We show that power variability both between similar devices and over time for a single device can lead to cost or savings estimates that are off by 15-20 % . Extending the coverage of measured devices and the duration (to at least one month) significantly reduces errors. Lastly, our experiences with collecting data and the subsequent analysis lead to a better understanding of how one should go about power characterization studies. We provide several methodology guidelines for the green computing community. The data from the Powernet deployment can be found at .