Gsense error rate?

Monitoring my HD with Hard Drive Health. Tonight got notice that Gsense error rate had dropped from 100 to 99. OK 15 min later got notice that it had dropped to 95. Google was no help in trying to get a handle on what this means. Is this common? What is Gsense and why does it have errors? Am I causing them? Although the threshold is "0" this big a change all at once has me concerned. Should I be? Any information or a link to info would be great.