Reading Alternator Output graph

I received this testing report with an aftermarket alternator I purchased for a project. Just want to make sure i'm reading it right and figured someone on here would probably know. The graph shows the Amp output vs RPM, this is the rpm of the alternator not the engine correct?
Since the graph doesn't start until about 1300 rpms I assume that's the speed when this alternator starts charging right?

Thanks!