The Counter n Aux signal indicates the first edge in a two-signal edge-separation measurement.
In addition, a counter’s Internal Output, Gate or Source can be routed to a different counter’s Aux. A counter’s own gate can also be routed to its Aux input.
Some of these options may not be available in some driver software. Refer to the Device Routing in MAX topic in the NI-DAQmx Help or the LabVIEW Help for more information about available routing options.