One thing to be wary of when using this library is floating point imprecision.
I left a unit running for a week sampling 10 times a second and was very confused when I came back as to why my average (over the last 50 samples) was very different to the actual current input.
Looking into the code, the RunningAverage::addValue function subtracts a Double and then adds a Double. Adding and subtracting of Doubles (and Floats) can lead to a huge degree of imprecision.
I'm not sure what the best solution is here, calculating the sum total every time getAverage() is called is the obvious one, but that leads to somewhat more function overhead.