It is very common to require placed dimensions related a datum other than Project Zero.
it is not wise to change Story Levels of a project to suit this other reference level as the working levels can become quite tedious to work with (compared to that of Project Zero).

An alternate method is available via the Levels & References dialog, allowing two additional references to be set up in a project and accessed via text components of either the standard Dimension tool or the Level Dimension tool.

To set up the Project Levels and References:

1. Go to Options > Working Units and Levels,
2. Enter a value in '1st Reference Level' that is calculated as "minus whatever the datum value is at Project Zero" is e.g. -96,000mm (for a 96m datum at Project Zero)

To apply the reference to a dimension:

1. Place a standard Level Dimension or an Elevation Dimension
2. Select the TEXT component of any dimension (you may select more than one text element before going any further) but NOT the dimension itself
3. Goto its Text Settings, and "Insert AutoText" "To 1st Reference Level"
4. Click OK
5. The selected text elements will now reference the -96,000 value, i.e if 3.5m to Project Zero, it will show +99.500m

The process of selecting each text component of a dimension is a tedious process, but is required as the regular dimension settings do not give access to the dimension text.

For more info on Dimenions and Gravity, click here to view a previous tip.