What functionality is missing? What is unsatisfying with the current situation?

  When working with timelines, I have found for three timelines so far that what I really want to do is to use a scale of years that is just a constant offset from UTD, reflecting a different year zero for that timeline but otherwise with years calculated in the same way. To think of a real world example, the timeline of ancient Rome was dated from the foundation of the city (ad urbe condita) (AUC) and if I had a world where the UTD of my main timeline was based on the current BCE and CE years, but wanted a separate ancient Roman timeline, I'd want one that used the same years but with 753 added, since Rome was founded in 753 BCE.   I'd like to have an optional offset in the advanced settings for a time line where you could have a plus or minus number that would simply be added to all displayed dates in that time line. If not entered it would default to zero giving the same behaviour as at present.   You would still enter dates as UTD dates for the world, just as you do now, but the timeline display would resolve, for example, -720 to 33 AUC by adding 753 and applying the local timeline specific suffix.  

How does this feature request address the current situation?

  If the displayed dates on a time line could automatically include an offset, it would have saved me a lot of work in manually calculating the same offset for every event and era and replacing the displayed header for each one with my own calculated timeline specific year. In the majority of cases with my timelines I would be quite happy with the automatic header display on eras and events, if only it could make this simple calculation (although, I've never been quite sure about getting the negative dates to look right without manual intervention but that's not the point of this request). As things currently stand I need to manually intervene for every event and era and find myself doing the same calculations over and over.  

What are other uses for this feature request?

  It just saves work for the author of a timeline that wants to track UTD but just with a different year zero. Letting the system calculate displayed event and era headers is usually better than manually overriding them, because they get automatically fixed if you change the dates and there is also less possibility for an embarassing calculation error when the author makes a mistake in setting manual date headings.