Does anyone have experience with peak flow meters? I have some questions about what's considered "normal". (read on) questions about?

I’ve posted about the breathing problems I have on here before, and last week I went to a respiratory therapist to get some tests done. She was the most helpful out of the 5 people I’ve seen for this. She said the tests were normal, but obviously I’ve still got something wrong going on. I got a better inhaler (she thought maybe the current one just wasn’t strong enough) and a peak flow meter to have some actual numbers and statistics to compare with.
She said for a female my height, weight, and age, my peak flow numbers should be somewhere around 400 liters per minute. Well, in the week and a half that I’ve had the meter I’ve never gotten above 370 lpm and I hardly ever get above 340 lpm. In one day, I can go from 300 when I wake up, to 320 at lunch, then down to 290 in the afternoon, and finally, just before I go to bed, I might be at 340. I’ve been writing down my symptoms, the peak flow numbers, and the time for this past week and a half. Looking back at the information, it looks like there’s absolutely no rhyme or reason to when my symptoms flare up, when the numbers are low, or whether or not they happen at the same time.

Sorry, yes, this was a lot of reading…
Here’s my actual questions:
1) Is it normal that my peak flow numbers fluctuate so much during the day?
2) The “normal” peak flow numbers for a female my size and age are about 400 liters per minute. I would think that I hardly ever get within 50 lpm of that is bad. Is it all right? Is this a bit alarming?

Thank you so much, guys!