You have to be able to look back at the previous 168 hrs (7 days) and be able to find a stretch of 30 hrs that you weren't on duty. You can be in the middle of a 35 hr layover on a trip or at home in your bed for two days. However, sitting on long call for 6 days in a row and not being called doesn't count towards the rest. Reserve is a hybrid animal, but in this situation it is not considered rest as it pertains to this rule. So if PBS builds you a reserve line with 10 days in a row and you never get used, on day 7 crew scheduling is going to have to cut you loose for 30 hrs.