From: ron@null.invalid   
      
   On Feb 16, 2021, Andy Burns wrote   
   (in article):   
      
   > Shine a red light and an infrared light through* a blood vessel onto an   
   > opto sensor.   
   >   
   > check the relative absorption of the two wavelengths in the blood, there   
   > is a correlation between oxygen saturation and their absorption ratio.   
      
   Why red?   
   TIA   
      
   Ron, the humblest guy in town.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)