Myself and 2 friends of mine have Foreunner 245. According the Garmin Forum replies all of us suffer of night apnea :)
A bad reading during the night is possible due to the unknown position of the wrist/watch, however even running manual tests all of us get unexpected values as 94% or so.
Therefore we collect 3 "regular" SPO2 meters and run 30 comparison tests:
Regular SPO2 tester:
- all 3 of us, 30 measurements (each minute) with 3 different testers = 98% - 99% (max reading range)
Forerunner:
- all 3 watches on all 3 of us, 30 measurements (each 3 minutes slower reading, 3 watches each) = 92% -99% max range
At our age, lower of 97% means health issues
Conclusions:
Now we ignore SPO2, even if unluckily we chose this model especially for this unreliable feature
We were hoping of a better management/calibration with a new Firmware, unfortunately after 3 years we didn't see any improvement about SPO2 performance .
