I picked this up for when I need to make simple depth measurements, or the outside/inside diameter of a pipe.  It doesn't zero perfectly, so I doubt it's truly accurate to .001" like a high end caliper would be.  But when you need to know if a pipe is 27.2mm or 25.6mm, this will work perfectly.  It might show "27.3mm" if you didn't zero it correctly, or opened it up too quickly, but if you know what you're looking for, and are careful with the measurements, this is a great tool.