Exercise 3: sample answer

Chapter 2 (sun and water): the shadow clock and water clock gave a way to tell the hours, but one failed at night and in cloud and the other drifted with temperature and flow.

Chapter 4 (the mechanical clock): the escapement gave a clock that ran by itself day and night, but the verge and foliot were inaccurate and needed constant resetting.

Chapter 6 (longitude): the marine chronometer let a ship know its position, but it was costly and delicate until later makers made it cheaper.

Which mattered most? One good answer is the pendulum clock, because it raised accuracy by a factor of many and made science and navigation possible. Another is railway time and time zones, because they changed ordinary life for everyone at once. Either answer is acceptable with a reason.