Some devices end up posting only time-based measurement data that requires a "previous" measurement in order derive instantaneous averages. Support this scenario by offering a "input data tracking" option on an Endpoint, that saves each input to a database so the "current" and "previous" values can be provided to each transformation.

This will require a known key for each endpoint; using a nodeId and souceId composite key provided as request parameters (NET-366) would be a good possibility.