offline members

[p.n.c]

I just got to know that when i add something like this in the template lets say footer or something

Members Online: $numberregistered
Guests Online: $numberguest

it would show me how many members online and how many guests currently on the forum

i wanna know if it is possible to show the offline members?

maybe do some sort of calculation to subtract number online from total number of members?

i dont know, help ?