How is AHI computed on machine?

[EeyoreJohn]

I am still less than a week on my CPAP machine, but I am already feeling better than I have in a while. The last two nights, I check the daily stats on the display of my S8 Elite. It reported AHI of 13.1 and 16.1 with a respective pressure leak of .24 and .36 L/s. (Using Swift nasal pillows - yeah... who knew? Thought FF mask would work best for me, but just goes to show what happens when you try diferent ones out. Definitely best when it is not too tight and the right size pillows are used!)

Anyway, I consider "how I feel" to be the best test, but I certainly have no problems finding out what might be better. Are the AHI numbers generated from the machine fairly accurate? And does anyone have a link talking about how the machine determines if an occurance has happened or not. I am only concerned because I am certain I woke up early this morning, checked the stats and it said an AHI of 15. I layed there for maybe another 30 minutes or so with my mask on to try and fall back to sleep, never did, but when I actually wrote down my stats after taking off my mask, it said 16.1 AHI. I am fairly sure I did not fall back to sleep or anything, but now I am second guessing myself as to why the AHI changed while I thought I was awake.