Marc,

Last year I called Mountain High because my EDS-D1a was annoying me
with the alarm sounding off more frequently than other units I used in
the past. According to the person I spoke to (I don't remember his
name), newer units have a slightly different oxygen vs. altitude
mixture and alarm threshold profile. This was based on empirical
studies conducted by MH in collaboration with the University of
Buffalo. This new profile acutally provides LESS oxygen supplied in
each pulse. He said that I could send my unit in and they would
re-program the unit so the alarm would not sound as often, but that the
level of supplied oxygen would also be thinner. I decided to live with
it and not send it in. I don't know if MH has tinkered or updated the
profile again since last year.