Switching from month to week calendar On iPhone one can switch to the week calendar view by turning the device into the landscape orientation mode. If you are on a day the week shown is the week, where the current day was. There are always three days shown in the week view. The first day of the week is either the current day or the selected day is in the middle of the three shown days.

If you are on month view things get complicated. I can't really predict which day will be shown. It works for most times if you go two rows up from last row (week) shown. But this doesn't work for all cases.

What is the system behind showing the first week calendar day when switching from month view?
If the current week is visible in month view, this week will be shown. Otherwise the week, which is in the view centre will be shown.