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An automated water dispenser fills packets with one liter of water on average, with a standard deviation of 5 milliliter. The manual says that after a year of operation the dispenser should be tested to see if it needs recalibration. A year later a number of filled packets are set aside and measured separately. It is found that the average packet now contains about 0.995 liters. Does the dispenser need calibration? Explain your answer.