A student uses a digital balance to determine the mass of an object. Its digital display reads 2.635 g. He keeps looking at the balance and it stays fixed at 2.635 g for half an hour. He then states, “The mass of the object is 2.635 g exactly. There is no uncertainty in this measurement because the last digit ‘5’ stayed constant and did not change over time.” Is he right? Is the mass of the object exactly known with no uncertainty? Explain.