Chiropractors have standards for validating a patient’s pain level. For example, a 10 normally means the patient is in enough pain to be unable to drive to work or move around the house. If you managed to visit the chiropractor on your own, your pain level is probably a bit lower. If a friend of yours had to carry you to the chiropractor’s office, then it’s probably a bona fide 10.
Another factor that results in differences in pain assessment is pain tolerance. Some people simply have a higher tolerance for pain, rendering such a scale grossly moot because facial expressions barely show whether or not they’re suffering from a pain level of 8 or 9. Chiropractors may find other ways to put the pain in perspective, if any.