It could explain that, however, setting it to low only means that when you run another application it "turns down" the SETI process to not slow down your other work. When running nothing else at the same time though, it's basically running it at High. That's what the priority part means. It should still read 100% most of the time even when priority is set to Low. When set to Low (and still running at 100%), it could either mean that SETI is using all 100% because nothing else is running, or that you have another application using 50% and SETI is using the other 50% - either way it should stil be pegged right near 100%.