An arrangement for dosing with a blade, in coating machines or similar, onto a running web of paper or cardboard carried by a roll in or with the arrangement. The blade is forced by means of a hold-down or several hold-down sections on the roll respectively the web. A transmitter transmits light, notably laser light. The blade features in the area between the contact line of the hold-down on it, and its contact line on the roll respectively the web, on its side away from the roll, at least one light-reflecting layer for reflection of the light ray directed by the transmitter at the layer. A receiver registers the position or angle of the ray reflected upon it by the light-reflecting layer of the blade. A controller is provided for controlling, dependent on the position signal of the receiver for the reflected light ray, the angular position of the blade, notably in its area between the contact line of the hold-down or the hold-down section and the roll.