I don't have a Skeets but I got the impression the zero shift was possibly a temperature thing. This would likely come from the outer tube picking up warmth from being held while the enter rod does not, thus making the gauge tube stretch & it would read Small. If this be the case a few cents worth of pipe insulation slipped over the shaft may well take care of the problem.
IF on the other hand something is moving, causing the shift it definitely needs fixing.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra