Symbols like "Diameter", "Radius", "Brackets" or "Prefixes" etc. are UNABLE to be shown on the Dimensions inside the square brackets when Dual_Dimensioning value is Primary[Secondary] or Secondary[Primary].
Practically, these [Dimensions] are not customizable except for "dual decimal places" and "Position" (only "below" or "to right").
I think that in case of dual dimensions, also the Dimension Property page should be double.
