You could have been at some point that was far enough within the range to be considered okay, yet still not be 100% okay.

It's a measurement I did every day I know how the value fluctuates and it was in the middle of the normal range.

A measure that is wrong in one particular case may still be the best measure available on a statistical level. I highly doubt that doctors would get better ideas of which therapies are good if they discarded this measure and instead used "does the patient claim to feel restricted breathing".

I don't claim that doctors should just replace FEV1 with "does the patient claim to feel restricted breathing". That's the kind of thing that doesn't need any reference experiences and is easily communicable via text.

I claim that the actual experience of interacting with a measurement in a involved way is important to train your intuition to be able to understand a measurement. If you don't have that understanding you are going to make mistakes.

If someone would give me a million dollars I might also produce a device that measures something better than FEV1 but that's not the main point of the argument. But that would be me wearing a bioinformatics hat and that's not the main hat I'm wearing in this discussion.