# Which mean to use to find the average of measurements given in the form of “per period”

Let's say I made several measurements on my gas consumption.

• $$2$$ m$$^3$$ per day
• $$1$$ m$$^3$$ per day
• $$1.5$$ m$$^3$$ per day
• $$2$$ m$$^3$$ per day

What is the average daily consumption of gas?

I can take arithmetic mean and it would be easy, but I've read a text in one statistics book where it says than in case of measurements in the form of per something (like in the above per day) you should use the harmonic mean to find the average.

So which mean should I use here?

You should be using the arithmetic mean as it would fit best in this situation. Typically, The harmonic mean is used where the numerator of the quantity we're interested is somewhat fixed, for example average speed when you travel from A to B at $$x$$ kmph and from B to A at $$y$$ kmph. During this average speed is equal to distance(numerator) divided by time(denominator). here the distance is same during both trips.
The Arithmetic Mean is used when the denominator is a fixed quantity for example if you travel for $$1$$ hr at $$x$$ kmph and $$1$$hr at $$y$$ kmph.