`get` methods normally just return something that is already calculated.  The normal convention would be to use `calculateFlux` here, since it requires a non-trivial calculation.  

The reason for this convention to help the user remember to cache the answer if they are going to use the result multiple times rather than just `getFlux` again when they need it again.  Seeing the word `calculate` is supposed to help remind them that the call isn't cheap.