Can't be adjusted, and unless it's leaking internally (disconnect from the back of the unit, hold some airspeed by compressing your finger over the hole and pressing; it should hold IAS and not leak down. Over time, we've found that just about every instrument sent back for "bad IAS" is basically spot-on in calibration. This means that it's sensing IAS correctly based on the pressures generated by the pitot/static sources. It's usually those that aren't perfect. This is a problem for lots of folks though, even LSA manufacturers (this is a point that the FAA has actually raised - finding good pitot/static locations). At the end of the day, though, that exact number doesn't critically matter except for finding your stall and other critical airspeeds.
