I am working on a project that requires ~.01g sensitivity to detect very very small changes in weight, but the actual measurement is irrelevant, it just needs to be consistent. For example, if I place a toothpick on the apparatus, I'd like to see a measurable difference. Based on the work I've done so far and what I've read, this is not easy (or cheap).
So far I have used a 5kg load cell with an HX711, which appeared to work until I realized my data was being affected by temperature and humidity changes. I don't know how to account for these changes, so I put this method on hold. I also think the 5kg load cell is designed to only .05% accuracy.
My next attempt was to use some of that conductive rubber string to see if it would give me relative measurements, but it was not sensitive enough. I would have to add .5kg or so for the returned values to show any significant change.
Another idea I had was to use a Raspberry Pi and a camera. I'd adjust the focus so that it became a macro lens, attach it to a fixed point on a spring facing a dithered/textured printed image then have it detect changes between each frame using OpenCV. Though, I think this is just a much more abstract and complicated way of mimicking what digital calipers do.
I have also considered using a spring and a range sensor (probably not accurate enough), and I think for it to be accurate enough I would need to use a laser displacement sensor (out of my price range). Contact measurement is OK, so my final trial would probably be to pick up some digital calipers and hook that up.
Am I missing any other method to do this or am I just plain out of luck?