Biometric access-control systems

Biometrics can't tell the identity of the individual. It checks the fingerprint, voice etc against what it has stored looking for similarities. If it finds enough similarities then it assumes the person is correct.

Yes, a person could be denied by the machine if the fingerprint doesn't have enough similarities to what it is checked against. For instance if the person moves the finger when it is read or places a different part of the finger on the scanner then the machine won't be able to find enough matches.

can you explain this part

" Such systems can be adjusted to minimize refusals of access to legitimate access- seekers"

They can be set to be less sensitive to differences, or allow the person more attempts before locking them out.

Because you are only checking a certain number of points you can adjust the number of points as needed.

Say the system requires 24 points be matched for similarites. If 50% of legitimate people are rejected then the system can be adjusted to only require 20 points or any other number. But the fewer points you require to be similar the more likely it will be for false positives where an illegitimate seeker may be recognized as if he was legitimate.