The summary-start-day placeholder specifies the first day of the week for which summary data is to be produced. The syntax for summary-start-day is as follows.
weekday-name | yesterday | today
mon•day[s] | tue•sday[s] | wed•nesday[s] | thu•rsday[s] | fri•day[s] | sat•urday[s] | sun•day[s]
The values are self-explanatory.