Greetings everyone. I'm working on a project that requires the very accurate measurement of distance varying between 0.500'' and 0.050''. I need to measure the distance within at most 0.010'' tolerance and give the value digitally. The read-rate is once every second. I'm on a very tight budget and there's obviously too many ways to do this than are readily countable- notably a micrometer, but i'd like to avoid that for certain reasons. Instead, I'd like to focus on the possibility of using a light sensor to measure the amount of light blocked by a barrier. The light source would be a LED and the barrier's movement would be coupled with the object's movement. I'm envisioning a ~0.625'' diameter, black tube with a LED at one end and a photocell at the other with a slit in the tube for the barrier to move up and down in. My question is whether or not anybody has had much success with measuring such slight differences in light levels using commercially available, cheap photoresistors or photocells. I'm also curious of what some of the challenges for practical application might be. Thanks.