I don't think taking instantaneous values instead of averaging will work out too well. For reference I've attached a screenshot. It has sampled values at every second on an unloaded computer and then with running prime95 for cpu stress testing. The load tends to peak and fall.

>Is it exactly the same thing on Unix (load average)?

Indeed it is: https://en.wikipedia.org/wiki/Load_(computing)#Unix-style_load_calculation

"An idle computer has a load number of 0 (the idle process isn't counted). Each process using or waiting for CPU (the ready queue or run queue) increments the load number by 1."

From what I can tell, the number of processors are dealt with the same way as on Linux, that is, a single core processor is overloaded when the load is >1 and a quad core processor is overloaded when the load is >4