are instructed to breathe into a hole which leads to an analyzer
that measures and indicates on a screen the level of carbon dioxide
in the breath. The body makes carbon dioxide when it uses energy.
The food people eat is combined with oxygen to generate energy.
This process produces carbon dioxide as a byproduct. This carbon
dioxide is exhaled in the breath. Here, the gas analyzer measures
the carbon dioxide. The levels indicated on the screen are about
120 times more than are found in air.