For the ScaleBar to function correctly, it is important that the MapUnit is set to whatever unit the Map's SpatialReference is using. By default the SpatialReference is automatically defined by the first layer with a SpatialReference in the layer collection.

Unlike the DisplayUnit which users see on the ScaleBar Control, the MapUnit is based upon the geographic data that is loaded in the Map Control. Geographic data can be stored in various formats that are most suited its purpose. Some examples of common common native formats of geographic data include Decimal Degrees for the Geographic projection, Meters for the Universal Transverse Mercator (UTM) projection, and Feet for the State Plane projection.