Not very useful. The readings are all over for various materials. Many perfectly dry materials (like drywall and wood) give mid-range readings, in the yellow zone. It cannot be calibrated for correct readings with any given material, so you don't know if a high reading means moisture or is just normal for that material combination. You need to calibrate it against a known-dry piece of identical material(s), not always practical.The auto-off feature is ridiculous. It shuts off after 1, 2 or 3 minutes without regard to measurement. It will shut off while measuring. Even the cheapest tools I own are smart enough to shut off AFTER 1 minute of INACTIVITY. Unacceptable at this price point.