Springs

Close view on the coils, as well as the springs that return the needle to zero. The positioning of the needle for calibration is achieved via device that looks like a flat head screw on the outside, but actually adjusts the position of the outer edge of the spring.  There are two springs, one to return the spring to 0, and another to retard it's forward motion, and arrest any momentum that may cause the needle to move further than it is supposed to.