def original(tag, replacement)
      original = nil
      if @dictionary.key?(tag)
        original = @dictionary[tag].key(replacement)
      end
      return original
    end
def original(tag, replacement)
      original = nil
      if @dictionary.key?(tag)
        original = @dictionary[tag].key(replacement)
      end
      return original
    end
Retrieves the original value used for the given combination of tag & replacement value.

 @param [String] tag the tag string (e.q. '0010,0010')
 @param [String, Integer, Float] replacement the replacement value (e.q. 'Patient1')
 @return [String, Integer, Float] the original value of the given tag