Changing the name of the default Calendar in Outlook?

I encounter the same problem. This is really bothersome if you have multiple calendars and try to run all of them. It takes extra cognitive power to see that it is the right calendar (by checking the e-mail behind it). It was never a problem for me before, working a multiple companies at the same time, doing volunteering work and having private agendas. 

Now, I need to take an extra look. 

I can't imagine having multiple Outlook accounts, as they'll all be named "Calendar", luckily there's Google. But it motivates me to convince everyone I work with not to use Outlook, as it will mess up my calendars and hinder me in my efficiency.