Silly Co2 Question

Hi all i have a silly question to ask so please excuse my stupidity
i bought a gunson gas analyzer as the rangie seemed to be going through a lot of fuel and the instructions tell u to calibrate it in open air first by turning the control knob till it reads 2% co2 which i did but does that mean that 2% is now your zero mark and if u wanted the mixture to be 1.5% for example u would set it to 3.5%?
thanks.

no you still have to adjust the engine to get a reading of 2% weird as it seems. if you read yer instructions it will tell you somewhere that the abient air has a co² content of 2%. the one i have you just leave it running for 5 mins in open air and it sets itself.
slob

thanks for the reply i guess that means i've set mine at 3.5% better adjust it back then as thats a bit rich.

thanks again