How to measure the distance between 2 points accurately Does anybody know how i would measure the distance between two points which will be no more than 50mm apart with accuracy to 1mm? 

I want to record the distance between the two points in a database over time at frequency of 1 datapoint for every second.

Anybody know what sensors could do this?
want to measure the movement of 2 points on a material surface as it is stretched and released the points move apart and towards one another. The points are real and tangible. This of pins in cloth and we want to measure the distance between the pins.


If the two points can be made then you could use an Ultrasonic range finder. you could have one point be a wall (use balsa wood or something light) then the other could be the range finder. You might have to do a little bit of engineering for attaching the range finder to the pins on the cloth, but I believe it's doable.

heres an amazon link for a generic arduino range finder: http://www.amazon.com/RHX-Ultrasonic-Distance-Measuring-Transducer/dp/B00F6KLLGG/ref=sr_1_2?s=electronics&amp;ie=UTF8&amp;qid=1439459256&amp;sr=1-2&amp;keywords=range+finder+arduino