[mrtg] CPU: Active vs idle

[Tasslehoff Burrfoot]

Hi all this is my first post on this list.
I want to ask a questione about monitor active CPU against idle CPU.

Around the net I found many examples about user cpu vs idle cpu, or 
every other single cpu value against idle cpu, but nothing about the sum 
of all these values (ssCpuRawUser+ssCpuRawSystem+ssCpuRawNice) vs 
ssCpuRawIdle.

I tried something like this but without success:
(Target[cpu]:ssCpuRawUser.0&ssCpuRawIdle.0:public at server + 
ssCpuRawSystem.0&ssCpuRawIdle.0:public at server + 
ssCpuRawNice.0&ssCpuRawIdle.0:public at server)

Is It possibile?

Thanks

Tasslehoff Burrfoot