code: private static Integer getSlotOffset(AisExtractor extractor,
  			int slotTimeout, int startIndex) {
  		if (slotTimeout == 0)
  			return extractor.getValue(startIndex + 5, startIndex + 19);
  		else
  			return null;
  	}
docs: Returns slot offset as per 1371-4.pdf.
  
  @param extractor
  @param slotTimeout
  @param startIndex
  @return