Most people like to think of Day 1 as today, which means Day 2 is tomorrow, Day 3 the next day and so on. This is the easiest and best way to use PeakAlert if you have saved the actual sleep you had last night or your default sleep is the same or similar as you get every night. In short, the easiest way to use the app is to think of Day 1 as “today” and each following day just adds one more day from today.