An agricultural working device, such as a mulcher, is improved with a working rotor which is driven by a drive shaft and a cutting rail with a cutting edge which can be directed towards the working rotor. Sensors for acquiring parameters of working rotor and/or cutting rail are provided. An electronic control apparatus is provided with at least one encoder to set the cutting rail. A method for setting the position of a cutting rail of a working device, such as a mulcher, relative to a working rotor, is configured in such a way that the rotational speed of a drive shaft and the rotational speed of the working rotor are measured and compared with one another. When a ratio of the rotational speeds differs by a predefined threshold, a change in the position of the cutting rail is brought about.