A plotter (1) for depositing an amount of liquid on a medium (3), said amount being determined by a unit of length. Said plotter includes a tubular pen (5) mounted on a pen holder (6) which is provided with a first device (4) for moving the pen relative to the medium. The first device is arranged to effect writing in a first direction (43) by the pen on the medium, and the end of the pen that engages the medium comprises a notch (2) forming an interstice between said end and the medium which gets progressively larger in the direction opposite the writing direction.