Hard Disk Sentinel showing 98% health, despite having no bad sectors?

[Man]

Pretty much the title, really. I recently checked my HDD with HD Sentinel and it was showing 98% health. Worried, I ran a full surface scan with 'auto repair' option which took a long, long time but as it turns out, my disk has zero bad and damaged sectors. But despite that, HD Sentinel is still showing 98% health?

 

I'm stumped. What can be the reason? Does it means there's a problem with my HDD's read/write header or something? The disk is pretty old with lots of hours so I won't mind replacing it but it's the data on it that's extremely important to me and I can't replace it at the moment, thanks to the pandemic. 

 

Any ideas?

 

 

[Murasaki]

Could be basing it off of specific S.M.A.R.T. values. Check them to see if theres something in there.

[Levent]

That is a cracked version of HDD sentinel if I ever saw one (because 5.4b is ancient). Anyways, "health" of the disk is useless, check logs to see if there are any bad sector related errors, otherwise dont worry any more than keeping your data on a HDD. I have one disk that 2600 days of power on time (w constant 70% health reading) and rest of my disks are all above 1400 days of power on time.