The correct way to average rates (i.e., inverse-time metrics) is to apply the harmonic mean, not the arithmetic mean.At least that's what the classic computer performance texts, like Arnold Allen (1990) and Raj Jain (1991), tell you.
My comment wasn't too emphatic though because the examples in those books do not refer to averaging monitored data, i.e., time series data. So, I wasn't completely sure about what I was saying. Good thing too, because the usual form of the harmonic mean doesn't work for time series! That, it turns out, is a very subtle subject and why I decided to use the slide format above to reveal my progressive technical understanding about what does work.
I'll probably have more to say about all this at the upcoming Guerrilla Data Analysis class. In the meantime, comments and questions by all are welcomed.