According to Article 10 of the Code for the Detection of Hair Samples of Drug-related Personnel: the hair samples within 3 cm of the hair root end are positive, indicating that the tested personnel have taken drugs within 6 months before the date of hair sample extraction.

It can be seen that the standard of drug detection in the police station is to detect hair within 3 cm of the root end, and the time for drug detection is within 6 months.