That's a reasonable price Bert... the readings are + or - 5%, from the 1% scale, still accurate enough to tune with... any mention or precautions regarding oil vapor using pre-mixed fuels, or 2 stroke oil injection... the water separator will catch some oil vapor, but I would still take measures to protect the sensor from oil contamination.

It will also show a change in CO with base ign timing changes, especially with your custom cam profile grind & valve timing changes you made with that particular putt putt boat engine... post another video when you get it all setup, I enjoy watching your boat projects.