I have been reading message boards for people who suffer from visual impairments and one discussion topic I found was how difficult it is to use rulers. The problem, especially with centimetres and millimeters, is that while the numbers on a ruler can be made bigger, the unit of measurement is fixed, so reading millimeters if you have problems with your sight becomes difficult.
Check out the New Rule. The solution is to have bigger numbered, higher contrast measurement bars that a sliding pointer runs along, displaying the millimeter measurement as numbers on a wheel inside the sliders housing. An arm inside the slider rests against the track and clicks each time it passes over a tooth in the track giving tactile and audible feedback of each millimeter although the designer admits the track would need more teeth than the prototyped version shown here. The second innovation is one edge folds over on a hinge. This turns it into a calliper so that accurate measurements can be taken quickly and easily. This was intended to make it easier for someone with poor sight to measure marks on paper as well as objects.
Designer: Product Tank