Set class dimension in a graph

[#1]

Hi,

I've a problem to make a class in a graph.

I wanto to count the event that happend in a range dimension. I've tried with class function, but it makes the same class range, what I wanto to do it's a graph with the range 0<x<72, 73<x<1392 and x>1932. How can I do?

Thanks in advance,

Fulgenzio