Number of online user In Server Manager.

Hello,

I'd like to store the number of online users by instance in order to analyze the performance of a load balancing technology our client has just installed. Like shown in this screenshot, the Server Manager displays the number of online users at the moment:

Since our client has 2 Production servers, I'd like to know from where does the Server Manager get the number of online users for each Instance?

Another question is : is there a way to store this information and visualize it (like a histogram plot showing the number of online users per server)

Thanks in advance for your help.