why health 80% not 100%

[di_ra]

i bought this hard disk and checked it i found it 80% health please help me know reason of health 80%

[hdsentinel]

The reason is dispayed in the text description, which shows the type and amount of problems happened during the lifetime of the hard disk.

In this situation the "Reported uncorrectable errors" attribute (and the problems reported by that) is causing the lower value.
I suggest to check the link displayed in the text description which shows the most common cause of this: cables/connections.

Verify those - and also perform some tests as described at http://www.hdsentinel.com/faq.php#tests
which are ALWAYS important to be done especially if you buy an used hard disk and especially if the status is not perfect.
And if the tests reveal no problems, the error counter and the health does not change, then you can manually reset that attribute in Hard Disk Sentinel to restore the health and be notified only about possible new issues with the hard disk.

[di_ra]

thanks
it's slim hard disk for laptop no cables and i will try extended self test

[hdsentinel]

In laptops/notebooks the connection can still be problematic.

The extended test is a good option for start, but not enough.
The short/extended tests run the hard disk "internally" to verify if ifs components are working in general.
However, these tests do not perform data communication between the hard disk and the system at all (except by sending status/progress indication) so if there is chacne for data communication problems, the Disk menu -> Surface test -> Read test may be better option. As it scans the complete surface and sends the data back for the system (so transferring high amount of data) it can be better used to verify if there are any further problems, increase in error count - or if the status is now stable.