Reference Sources
As detailed in the CFE portion of the manual, some Data Field Categories can be referenced as a source of data rather than directly selecting a sensor's data field. For instance you might have 3 GPS units with varying levels of accuracy or preference. By referencing the Latitude category SCS will automatically provide best GPS as a source at any given moment.
For obvious reasons there are plenty of use cases where the above is preferable. However, when referencing a category you aren't always aware which sensor is truly providing you the data. To get a holistic view you can reference this portion of the Settings page to determine WHICH sensor is providing the feed for each data field category at the moment.
The first column of the grid will have the Data Field Category being referenced. The second and third columns will tell you which actual Data Field SCS is currently using to serve up the sensor data stream for the given category.
You can expand each row/category to see the list of potential sources, the one highlighted in green is the currently active source.
If - None - is displayed then there are no Data Fields found in your configuration which have their category set to the given type.
If - Note Available - is displayed then there are Data Fields found in your configuration which have their category set to the given type but none of them are currently good enough (eg failing QA/QC checks) to act as a reference source.
If the category name is red then that category has no valid feed, do not use it as a reference in your templates until you assign at least one Data Field to it.
To modify which data fields are eligible for a Data Field Category reference you must use CFE.
See also: CFE - Physical Device Reference Order