Peak flow Dolly

I have to keep a peak flow diary for two weeks! I have a problem with my chest where my sternum curves in instead of being flat, see this link! It doesn't bother me that much most of the time but I have a tendency to be quite short of breath, so the doctor wants to check it out! Did a peak flow test with the nurse the other day and it was rubbish, must blow harder! I'll have to take it on holiday with me, probably a good thing as I plan to be walking lots so I'll get to see how bad it is, or rather, what's normal for me!