Method and device for bending a portion of an element in a bending machine (12) comprising a bending assembly (14), a supporting plane (18) and an electronic processing unit (32), wherein the bending process is filmed and displayed on a screen (36). The portion (24) is bent with a first movement of the bending assembly (14) to make a first bend of a nominal value. By means of reference indicator elements an angle of deviation is determined and the portion is again bent with a new movement of the bending assembly (14), taking into account the angle of deviation. All movements of the bending assembly (14) are acquired by a position transducer (15) and recorded by the electronic processing unit (32) in order to have a global parameter for obtaining an angle which corresponds to the nominal value, and in order to use the global parameter in subsequent analogous or similar bends.