17.01.11. Product Tank New Rule - 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 (here). 

The design problem, especially with centimetres and millimetres,  is that whilst the numbers on a ruler can be made bigger (See RNIB site here), the unit of measurement is fixed, so reading millimetres if you have problems with your sight becomes difficult  (as an example, squint at the image of a metal ruler on the right).  Electronic Callipers turn any small unit of measurement into a number, but you can‘t use them to draw a straight line.  So it seemed appropriate to try and create a combination of both a ruler and a calliper.

I still wanted a mechanical solution as it seems overkill to make it electronic and also because in terms of clarity, the contrast of printed plastic is still higher than a LCD display and much more cost effective than an OLED solution. 

My design solution is to have bigger numbered, higher contrast measurement bars, that a sliding pointer runs along, displaying the millimetre measurement as numbers on a wheel inside the sliders housing.  The slider runs along a track that rather than be concealed, is open to allow for ease of cleaning. 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 millimetre (the track would need more teeth than on the prototyped version shown for this to work properly). 

The second design innovation is to have one ruler edge fold over on a live 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, but I have found whilst using it that it is much more efficient than a ruler as I have the option of converting it into a calliper, taking a measurement, then flicking it back into a ruler and drawing a line on paper with the pointer in the same position, allowing for a smoother, quicker work flow.

I appreciate there are problems with the accuracy of measurement over distance caused by tollerance using a cog and track.  In the next version of my design concept, I will have the numbered wheel in the slider accessible from the back of the housing, so that it can be turned by a finger to 'zero' it anywhere along the length of the ruler.