Settings
Everything on this page stays in this browser.
Cycle
Factor in your cycle? Optional, and private to this browser. When it is on, the check-in asks where you are in your cycle. Only your own answers are used. Nothing is guessed from dates.
Cycle info stays in this browser.
Your data
Check-ins are saved only in this browser, so nobody else can see them. Calendar files are read in your browser and are never saved. Event titles are never stored.