Complex sentence: Generally, a units should be linked only if it is likely to be obscure (troy ounce, bushel, candela, mho, millibarn) or if the unit itself is being directly discussed (see use--mention distinction).
Split into simpler sentences: Generally, a units should be linked only if it is likely to be obscure (troy ounce, bushel, candela, mho, millibarn). A unit should also be linked if it is being directly discussed (see use--mention distinction).