What does nPercentile do in Graphite and how is it different from percentileOfSeries?

nPercentile : "Returns the n percent of each series in the series list."

This will convert every series you give it to a single value *, i.e. the nth percentile of that series (but it will output as many series as given as input).

* note that like everything in graphite, this single value will be returned as a series containing many times (as many times as necessary to fill the requested time range) the same value.

percentileOfSeries : "percentileOfSeries returns a single series of n-percentile values ​​taken over a series of wildcards at each point."

This returns one series that, for each point in time, contains the nth percentile of the different input series.