Abstract: For the accurate setting of machine tools, mechanically and electromechanically operating feeler devices are used, for example optical display means, which light up at the moment of touch contact with a surface to be machined. The accuracy of setting using these devices does not, however, satisfy the required setting accuracy in many cases. A method is provided, by means of the invention, in which a feeler head is slowly approached towards the surface or edge to be touched until the contact of the rotating feeler head with the surface or edge corresponds to a feeler head rotational angle (.alpha.) which is greater by a predetermined safety value than 180.degree. but is smaller than 300.degree.. The device for this purpose consists of a housing with an electrical voltage source and circuitry equipment for optical display elements, the housing being penetrated by a hollow shaft connected with one pole of the voltage source.