Dear Iamloco: I'm a respiratory therapist & asthma instructor. Each person is an individual and there really isn't a "set" reading even though in your peak flow box you will find a packet w/settings. I'll give you an example. For me, I do 600 - 650 easy, I'm 5'4", 128 lbs, don't smoke or drink and have no hx of respirtory problems. Someone who smokes even though they weigh the same & is the same age will not have the same reading. By smoking they are damaging their lungs. I also do routine breathing exercises just to keep lungs in good shape. Therefore, on a day that you think is a "good" day with no breathing problems (no signs of asthma or allergy symptoms & no other sickness), this is the day to set your peak flow meter. Stand (not sit) tall, take in a deep breath, and breathe out fast and as hard as you can in one hard blow. Do it 3 times. The best one will be your base line. After that, each time when you feel you need to take it, make certain you stand and do exactly as you did when you set the meter. Whether you stand or sit makes a difference in an accurate reading. Hope this info helps. The American Lung Association has some pamphlets if you need further info.
Info meant for educational purposes & not as med advice.