Put two dates next to each other and see where they agree and where they pull apart.
Readings written in languages other than English.
Send a single day to a friend without handing over your whole calendar.
An optional nudge the evening before, so a good day is not noticed after it has gone.
A calendar feed so your marked days appear in Google Calendar or Apple Calendar next to everything else.
Your planets and houses written out in plain English, so the Western side reads as clearly as the day marks already do.