And the Preview function is useful
To tidy up the post, use modify in the right corner of the posted message.
I was using a CO2 sensor at school today, measuring absorb. propperties of different zeolites and their absorbtion rates. Must buy one of those 
the linearity was great from 5000 ppm to 2 ppm CO2.
Next month I will be using a NIR. Analysing petrol fractions and doing multivariation analysis, to be able to determine octane number of petrol blends just from simple NIR readings (part of my bachelor).
This I will definetly port to my arduino!
Few red and IR-leds and narrowband ir-filters and a photodetector, tubing, pump...
Then mesure the octane number of the petrol in my car 