By the way.... anyone using Sleepyhead software (free). If you have one of these machines you can read your own card
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SleepyHead is open-source, cross platform, sleep tracking software by JediMark with a focus on monitoring CPAP treatment.
It currently works with data capable versions of the following machines:
Philips Respironics System One
ResMed S9 families
DeVilbiss Intellipap
Fisher & Paykel Icon support is coming soon!
You can also use Contec CMS50 (USB serial) oximeters, as well as ResMed S9's oximeter attachment.
SleepyHead is currently in Beta release..

I took a 90 minute nap after I got my new machine and mask and then popped the disk into my computer. It seems to show a 4.77 AHI. (5-20=mild, 21-50=moderate, above 51 severe)

And.... it showed all my events as being "Clear Airway" (Central).....

So... will be interesting to monitor this.