It is poor etiquette to hijack another topic I have moved it to its own, to prevent confusing replies.
Have you looked at filter node? It can be set to block messages on a percentage change.
If you supply an array with a set of readings including an outlier, You will probably get far more examples. (09/13 to 09/14 looks like a good data set to play with).
Any one who wants more ideas can look at this topic to Smoothing a value and check for extrems