Optical sensor reverse reading

[Robert.Wall]

A little more here:

LED pulse sensor problems

Try moving the sensor around very slightly on the meter, also rotate it on it’s axis (ie cable entry down, up,left and right etc) and/or angling it slightly whilst watching the LED. Since you have now observed this odd behavior I shall also share my findings (I didn’t want anyone thinking I’m even more nuts than they already did) I have noticed a strange situation, where I can move a sensor and position it to give anyone one of 3 outputs from the same pulsed light source, LED flash only, no …