The recent discussion here about CO2 monitors and the virtues of making your own v buying one led me to wonder, how much is a person's time worth? $10/hour? $20? $50? $100? $200? More?
If it takes 3 hours to make a CO2 monitor, including obtaining $50-$100 worth of parts/soldering etc./calibrating etc. — and your time is worth $50/hour — then the Aranet4, perfectly calibrated and ready to use out of the box for $250, is a wash.