Abstract: An automatic control mechanism for the thickness of an ink layer on a duplicator cylinder employs a sensing roller mounted for movement along a path which extends both peripherally and radially of the cylinder where the ink is to be measured and thus the drag on the ink pulls the cylinder to an equilibrium position where it just maintains sufficient contact with the layer of ink to be subject to that drag whereas any further movement will move it radially away from the ink layer to lose contact. The pivoting support for the sensing roller engages a switch when an extreme position is attained and this provides an "enough ink" signal.An adjustable biasing mechanism enables the position of the sensing roller to be additionally subject to a biasing selective manually by the operator to control ink layer thickness and another adjustment in response to the speed of rotation of the duplicator.