Fuente: WIPO "tomato" There is described a method for monitoring the quantity of packaging material accumulating in a buffer device (10) of a packaging material processing unit, the method comprises the steps of: - detecting a distance between a predetermined section (S) of a web (4) of packaging material loop (11) in the buffer device (10) during the accumulation therein and a fixed reference point of the buffer device (10); - receiving a first sensor signal (S1) indicative of said distance; - calculating the quantity of packaging material accumulated in the buffer device (10) as a function of the first sensor signal (S1).