Why is the volume of co2 production rather than o2 uptake an adequate measure of respiration?

To measure the rate of respiration, scientists usually utilized the volume of carbon dioxide produce rather than the volume of oxygen that was uptake. The volume of carbon dioxide is used for measuring the rate of respiration because it is difficult to gauge small changes in the concentration of oxygen. Also due to the presence of oxygen in the atmosphere, atmospheric oxygen can easily be introduce into the samples been used thus, making the results of the experiment invalid. The rate of respiration is tightly coupled together with the rate of cell metabolism, thus measurement of respiration via measurement of carbon dioxide also allows scientists to easily monitor the metabolic states of the tissues.