If the firmness of a burning filter cigarette is measured during a puff interval at a distance of 40 mm before the end of the cigarette's butt, it is of negligible effect on the results whether the cigarette has been extinguished immediately prior to taking the measurement or whether smouldering is maintained during the measuring action. This holds true, however, only on condition that mechanical smoking is carried out under standard Coresta conditions or with variable duration of the second puff, if the latter does not last longer than 4 sec. Under these circumstances, the temperature increase of the tobacco rod is very smalI and does not constitute a causal factor of possible alterations in firmness