Did you ever wonder how much power was consumed by executing a program? The Chameleon team recently implemented a feature that automatically collects power usage data on all low power nodes in the system. Instantaneous power usage data (in watts) are collected through the IPMI interface on the chassis controller for the nodes. This “out-of-band” approach does not consume additional power on the node itself and runs even when the node is powered off. Low power nodes for which power usage data are now being collected include all Intel Atoms, low power Xeons, and ARM64s. In this blog post we look at this new feature and use it to calculate the power consumption associated with multiplying two large Python numpy arrays.