The 5 second interval is not enough to show real server load.
Think of users that browse through the folders with some images, or that only download a file of a few MBytes. That will last more than 5 sec, so using outgoing speed may be full bandwith during this interval, even if there is really bandwidth available to serve other useres.
But don't waste your valuable time at this at the moment thinking about this, because there's no simple and usefull solution.
Even using a greater interval the value may not be usefull in the case of more users conected, as there is no way to know what users are doing:
I can have 3 users only browsing (generating less traffic than bandwith allows in 5 minutes). So we would have good value for available bandwidth, but:
Depending of the moment when we pick the value, they appear as 0..3 downloading users! If one of them (or a forth user) is really downloading for more time, all values get useless, not because the full bandwith is used, but because of the number of simultaneous download-users: There is no way to know with how much people we really have to share the bandwith, so any number would be useless to predict the available download-speed dividing the value using the number of downloading users (1+ (0..3 ?)).
Only more graphs which shows users conected/downloading over time could give more acurrate information. But that's exactly what I want to avoid: graph's and kbp/s are for techies, and i wanted a simple semaphore-like style (green, yellow, red) and/or an simple indicator (1 Mbyte download will last about 25 sec..) for non-techies.
Thank you.