I'm thinking about using two slits, a webcam and a laser to calculate distances for a project. Usually you measure the distances between maxima but this can be easily measured in a dark room using Matlab and it's image processing routines. I can create the slits and accurately measure them using an optical microscope. Is this a good or bad idea? Using error analysis, I think I can get the distance down to 1 part in 1000 so 1mm over 1 m away or .5mm over 2m away. Maybe I can combine it with a cheap interferometer and make it super accurate. Problem with an interferometer is that you can only measure within 1 wavelength. Any comments?