What does the C0/C9 function on the COA26 display do?

The C0 to C9 is a memory for the measured data that COA26 can keep. When at a certain moment a certain value is measured, this value will be stored in the memories 0 TM 9. 

As long as C0 to C9 is shown in the menu, this means that no carbon monoxide has been measured. 

If 'Alarm' is displayed with a value, carbon monoxide has been measured.