What would you do with a compass that didn’t point toward true north? Or a watch that never told the correct time? Or a car speedometer that told you that you were driving faster or slower than you actually were?
No matter how high-caliber your moisture meter (or composition meter) is, an instrument is only as strong as its calibrations. There’s a lot riding on getting a correct reading: Concrete foundations can crumble, stored grain harvests can spoil, and pharmaceuticals can degrade or become toxic.