A diagnostic method for analysing the operation of an automatic machine which processes products in the tobacco industry includes the following steps: introducing into the machine an endoscopic probe whose shape and size correspond to the shape and size of the products the machine is designed to process and which the machine processes as if it were a real product. During processing in the machine, the probe acquires data through a sensor of its own. The method also includes determining the positions adopted by the probe while it is being processed in the machine and associating them with the data acquired by the probe while it is being processed in the machine.