Marcus mentioned your reply to me, and I think I should clarify/give a little more information. Judging the number of pack years a person has smoked without questioning them involves more than just listening to them go through a series of breaths. Other information that informs my judgement includes the person's age (If I'm examining a 30 year old woman who sounds like she has jell-o filled lungs I'm probably not going to think she has smoked for 50 PY's), the way the person breaths (When at rest, what is the patient's shallow to deep breath ratio?), where different types of sounds located, and other nuanced indicators. If you are a little more tuned into these things like I am, you develop a pretty sharp predictive sense. Any pulmonologist worth his/her salt can do it, and competent and experienced respiratory therapists can do the same thing after watching a patient go through a short battery of exercises. Sometimes we act like pool sharks calling shots. It can be fun.