The ‘Keyway Ruler’ is a comment on the struggle of ‘flipping’ between metric and imperial measurement. The units are kept separate on different faces of the ruler blade to avoid any confusion. The act of ‘flipping’ the ruler between the units has been developed by an investigation of ruler profiles and features that found on existing products. The ‘rolling’ allows the ruler to be easily removed from a page once a line is drawn reducing the risk of smudging. The ruler is available with a brass ‘keyway’ profile which can then be fitted with a steel, walnut or beech blade.