The Reference mode menu lets you select between Global, Local, and Additive Reference modes. The Additive Reference mode is only available when you are in Rotation mode.
Reference modes affect how the translation, rotation, and scaling values of an object are displayed. See Reference modes.
Activates Global Reference mode, so the selected transformation values of an object are displayed relative to the center of the scene (the global axis).
Activates Local Reference mode, so that the transformation values of selected object are displayed relative to the center of the object, or from the center of its parent, if it is parented.
If the selected object does not have a parent, the values of Local mode are the same as Global mode.
Activates Additive Reference mode so that the selected objects transformation values reflect its actual coordinates on the current layer only. This is useful when you are working with FCurve values.