Counting number of guests online

I’m currently using eldorado forum which shows the users that are
currently logged on. I wanted to also add the number of guests that are
currently viewing the site.

What do you think is the best way to go about this and where should I
keep track of this number?

I’m thinking I would have to keep track of the ip addresses that are
currently connected but then would i just subtract the number of logged
in users from this to get the number of guests?

Can someone point me in the right direction? Thanks!

I too am looking for a way to count the number of guests visiting.