This four pulley parallel motion ruler can be utilised on any flat surface (office table/kitchen table/drawing board etc.). The device comes with strings and metal clamps for temporary attachment. Both sides are beveled with an inking edge. Made from 4.5mm thick clear transparent acrylic sheet. 61cm total length (printed scale to 57cm). Transparent handles allow for complete overview of drawings below the ruler. Instruction sheet included. A cost effective and extremely practical alternative to a conventional drawing board. The ruler is quickly and easily erected when required - likewise simple to dismantle and pack away after use. Position the 4 clamps in alignment with the straight edge’ pulleys. Tie and cross thread the string from one corner clamp to the opposite corner clamp on a diagonal between the pulleys. Repeat for the other diagonal. Tension further if required. Once mounted the square edge will run parallel on its path across the surface.