Final answer:
To correct a mistake on a PCR, you should draw a single horizontal line through the error, initial it, and write the correct data next to it, maintaining an accurate audit trail.
Step-by-step explanation:
If you inadvertently write the incorrect blood pressure reading on a Patient Care Report (PCR) and need to correct this mistake, the appropriate action is to draw a single horizontal line through the error, initial it, and write the correct data next to it. This is a standard practice in medical documentation to ensure that the record is both accurate and has an audit trail of any changes made to it. Using correction fluid or attempting to erase the error is not advised as it could cast doubt on the integrity of the patient's medical record.