rate() is the function to express a nonNegativeDerivative. This document is the best source of information when looking through Wavefront query language capabilities: https://docs.wavefront.com/query_language_reference.html.
i used the rate function, but it doesn't give me the same graph as of graphite. the values are different when used the non derivative function in graphite and rate in wavefront.
this is graph from graphite. the value is in mil here.
graph from wavefront. the max value is 44k in wavefront.