This may be a bit stupid, but... EDIT yes it is a really stupid question which I should have guessed the answer to, but will leave it up for fellow blondes
Had norovirus yesterday (ugh, not recommended, but glad it didn't last too long). As a result of throwing up way too many times, my chest muscles are rather sore today. I tried to do a PF a couple of times but discovered it hurts (especially round the bottom of my ribs) and comes out on the low side even though I don't feel particularly SOB.
This seems to imply that I'm normally using these muscles to do a PF, and wondered if this is actually how you're supposed to do it - would using these muscles not be adding an extra push and messing with the measurements? Or maybe it is completely normal and I'm only noticing now, but it's odd that I'm getting between 66% and 75% when not particularly symptomatic given it usually refuses to drop much when I AM symptomatic!
Another PF confusion, ugh. I wish they'd invent a better home measure, as there still seems to be so much store set by it and I never really trust it properly.