All the above is correct but here it is listed out:
You are paid the greater of:
5 hours per DUTY period. (again, a 4 day trip may only have 3 duty periods)
or
1 hour for every 3.5 hours time away from base.(trip rig)
or
1 hour for every 2 hours of duty time (ie 12 hour duty day pays at least 6 hours) (duty rig)