CareFusion MicroCO Operating Manual page 22

The gas is supplied in convenient, disposable, aluminium aerosol cans
(Cat. No.36-MCG020).
To carry out the calibration locate the calibration switch on the right
hand side of the instrument as shown below.
Serial
port
Push the slide switch to the CO - PPM position and wait for the unit to
display zero.
Screw the control valve firmly onto the cylinder and connect the gas
supply as shown below:
20
Calibration
Switch