[rolleiflex]

The cheap SPO2 devices are calibrated on fair skin. If you have a darker complexion there is a known measurement error. If you are at 91% and feeling fine you are probably fine. Your body has a better SPO2 sensor than anything man-made.

[kumarvvr]

Damn, I am brown and I guess I have to take that as a 3 - 5% error?

[rolleiflex]

That is correct. See here: https://pubmed.ncbi.nlm.nih.gov/18048893/