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, pharmaceuticals can degrade or become toxic.