Using the click-to-zoom function
When zooming in on a peak, the peak may appear to be higher in value as it is zoomed in on. This is because the time axis is compressed as there is longer time periods shown, each interval is a longer period of time and therefore the power averages are lower. A more detailed description can be found here.
Since firmware version 2.1, the eGauge graphical interface supports mouse-based zooming. This is a useful feature when trying to isolate spikes or display a specific time period.