Final answer:
Per FMCSR 395.8(f)(1), the Record of Duty Status (Log Book) should be updated at each change of duty status.
Step-by-step explanation:
Per FMCSR 395.8(f)(1), your Record of Duty Status (Log Book) should be updated at each change of duty status. This means that whenever there is a change in your work task or activity, you should update your log book to reflect the new status. For example, if you start driving, you would update your log book to indicate that you are now in the 'driving' duty status. Similarly, if you stop driving and start taking a break, you would update your log book to indicate the change.