SWP: Figure 6 presents the day-to-day error of SWP
for a single representative user. Three days are shown to have
noticeably larger errors than the rest - the 3rd, 5th and 6th
days. On the 3rd day, we find the user forgot to inform SWP
when sleep began, this error is only corrected by the user in
the middle of the night. Later in the week - on the 5th day
- we find the user stopped the app because the phone had
become very hot. Finally on the 6th day, the user reports the