Abstract: A support structure defining a flat support surface for supporting a web material includes a number of beams, each having a cross-section elongated in a first direction normal to the support surface. The beams have a ruler edge extending in a second direction in parallel with the support surface, which is defined by the ruler edges. The support structure includes a number of adjustment mechanisms for adjusting the positions of the ruler edges in the first direction. Each beam has a base part and a ruler part, the ruler part defining the ruler edge and being connected to the base part by at least three adjustment mechanisms distributed over the length of the beam. Each adjustment mechanism includes a lever that is pivotable relative to the base part about a fixed fulcrum, is connected to the ruler part, and has an adjustment arm with an adjustable free end.