In order to get reliable CO2/CO ratios in the equipment, CO2 and CO values should be
corrected (incremented) first for possible CO2 absorption from atmospheric air, and for the
CO2 and CO background values (see 6.1 and clause 9), resulting from the ageing of cellulosic
insulation, overheating of wooden blocks and the long term oxidation of oil (which will be
strongly influenced by the availability of oxygen caused by specific equipment construction
details and its way of operation).