Four possibilities that occur to me are:
1. SH directly copies and reports the AHI number that is calculated and displayed by the particular PAP machine one is using;
2. SH calculates the AHI number itself but, to do so, it uses the same AHI-calculation algorithm that is being used by the particular PAP machine one is using;
3. SH uses its own algorithm to calculate AHI but it does so based on the numbers and types of events (OA, CA, H, RERA, etc.) that the particular PAP machine has flagged;
4. SH uses its own algorithm to calculate AHI and to do so it independently assesses and flags what it defines as an OA, CA, H, RERA, etc. based on its own independent assessment of flow curves, etc.
One reason I am asking this question is that I am currently trying to compare the treatment efficacy of two different PAP machines that I have, and to do so with reference to SleepyHead I need to know in general terms what SH is doing. For instance, I've been told that I can't directly compare the AHIs displayed on my two PAP machines because they use different algorithms. Does this same lack of AHI comparability across PAP machines (brands) "infect" SH's calculation of AHI, making it impossible to directly compare the AHIs as displayed by SH? I know, of course, that ultimately the raw data depends on what the particular machine stores and thus uploads to SH, but I'm interested here in what SH does with that data which leads ultimately to its own reporting of the AHI number.