I am missing a sensor that would take input from another sensor and display the derivative of that sensor.
I.e. for a sensor displaying distance (e.g. a car odometer sensor), it would display speed. For a sensor displaying amount of data transferred (for e.g. a modem), it would display data transfer rate. For a sensor displaying temperature, it would display temperature change. Etc.
Would that be usefule to anybody else? Is this already possible or does it already exists?