Measuring small distances

hey all
i know that you can use ultra-sonics and also lasers to calculate distance, but how accurate are these methods?
i.e what sort of range are we looking at?

Is there any method that could be used to measure differences of a thou or less, that are not overly expensive to employ?

thanks alot
Kane

Keyence manufactures a multitude of distance sensing and measuring equipment. I've used their equipment. Accuracy depends on a lot of things. Certainly the accuracy of the sensing/measuring system will help to define a limit of expectations however the application plays a big part too. I'd recommend researching various manufacturers offerings to see what they are able to do. While the devices may not be affordable it will give you some sense of the technology and how far it can be pushed - given that these manufacturers have lots of experience, relatively speaking.