The calendar widget at the top-left doesn't show days of the week, so you have to work out whether the week starts on Monday or Sunday (or click on a day to get the main pane to show the full info).
If adding a row showing "M T W T F S S" above the widget isn't desirable the empty squares beyond the start and end of the month could be used to show the day of the week.
mock up showing days of the week in blank spaces
<img alt="cal.png" src="/fedocal/issue/raw/files/1c623c1a139f62f496c5d5542a2241944c1accb22d655475b63576b76e538287-cal.png" />
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