Source "(N)RPN value"
This source reacts to incoming non-registered (NRPN) or registered (RPN) MIDI parameter-number messages. The higher the emitted value, the higher the absolute control value.
(N)RPN messages are not widely used. If they are, then mostly to take advantage of their ability to transmit 14-bit values (up to 16384 different values instead of only 128), resulting in a higher resolution.
RPN checkbox
If unchecked, this source reacts to unregistered parameter-number messages (NRPN). If checked, it reacts to registered ones (RPN).
Number field
The number of the registered or unregistered parameter-number message. This is a value between 0 and 16383.
14-bit values checkbox
If unchecked, this source reacts to (N)RPN messages with 7-bit resolution, including increment/decrement messages.
If checked, it reacts to those with 14-bit resolution. In practice, this if often checked.