Answer:
If I set my alarm to read 8:10 when it is really 8:00 (i.e., it is 10 minutes fast) and the alarm goes off each day when it reads 8:10, it will be reliable but not valid.
Step-by-step explanation:
If I set my alarm to wake me earlier than I need to be woken, it might be in order to give me enough time to adjust to the alarm, and be awake enough to get out of bed before the normal time I need to be out of bed. This method is very reliable, as there is a very little probability of me waking up late, since I have a 10 minutes head start everyday to get out of bed. The problem is that this method is not valid, since I now actually wake earlier than I am supposed to. The extra 10 minutes can actually lead to a disorientation with time.
