I was taking my peak flow yesterday and just wondering why I always get higher at the gp, than I get at home. First I though it was just down to the pf meter, but then I thought, hang in the cardboard tube at the gp, is wider than the plastic mouthpiece I have on mine. So the scientist in me thought, hmm experiment. So blow on the plastic mouthpiece, get 450, take mouthpiece off and seal lips round the bit that's left, get 500.
Now am I doing something wrong, or is the size / shape of the mouthpiece influencing the pf result? My highest at home reading is 550, at the gp it is 570.