Update (January 4, 2017):
You can recently make specifying a PR mandatory.
You can do this by, as an administrator, using the right-hand drop-down menu --> 'Online registration settings' --> "Mandatory specified best performance period" to specify a start and end date by which the athlete must have achieved the performance.
Once you set a start and end date, it becomes mandatory for registrants to fill in all fields for their best performance.
We have had these fields mandatory in the past, resulting in registrants entering nonsense/random numbers.
So we are no longer mandating these fields. An athlete/registrant usually disadvantages himself/herself by not filling it out correctly, because it puts him/her in a less enjoyable heat (i.e., no heat with equivalent competitors).
This has been automatically translated into English