if (this.data.size() > 0) {
            for (int index = start; index <= end; index++) {
                TimePeriodValue item = (TimePeriodValue) this.data.get(index);
                TimePeriodValue clone = (TimePeriodValue) item.clone();
                try {
                    copy.add(clone);
                }
                catch (SeriesException e) {
                    System.err.println("Failed to add cloned item.");
                }
            }
        }
        return copy;