A simple pendulum is known to have a period, T = 1.55 s. Student A uses their smartphone stopwatch app to measure the total time for 5 oscillations and divides that by 5 to report an average period of T = 1.25 s. Student B uses the same technique but goes old school and whips out his grandpa’s analog stopwatch to come up with an average of T = 1.5 s. What is the most probable source of error that explains the different results?