Coming back to this, I'm still unclear.
When I want to share a calendar, am I right in thinking that I can enter any kind of email address into the list of people to share with, or do they have to be Google email addresses?
Now obviously these people need Google accounts to be able to see the calendar, even though the addresses I've added for sharing purposes may be work email addressed, so... let's say I send the people in the list a link. They then click the link and... then what? They then have to (I presume) log in to their Google account. But how does Google know that the people logging in are the people with non-Google email addresses as above?
IYSWIM
I tested this yesterday with someone, and the person (non-Google email address) was able to view the calendar from the HTML link that I'd sent after logging in to their Google account. But for another colleague, the link did not work until I added them using their Gmail address.
I don't want to make the calendar public.