I don't know how this tool works, but it's magic. It is very easy to use and causes no damage to the surface being tested. The hardest part of using this tool is finding a flat surface that fits the entire unit. Most of the time that's not a big deal because floors, walls, wooden boards etc. are pretty flat. My challenge was with crown mouldings. The sensor is a small patch on the back of the meter, but to get the sensor to lie flat on the wall you need the entire unit to lie flat.
Fortunately this is easier to use than a stud sensor because you just need to find some orientation that gets a portion of the sensor into contact with your surface of interest. In addition, you can see the readout change as you approach the surface so you can tell how well you are doing. Measuring the moisture level of a dry area helps to determine if you are getting good enough contact to the region of interest.
For my need this was much better than a pin type meter because it did not drive any holes or pinpricks into the surface of my walls. Because it causes no damage I was able to test many areas to determine what dry was before getting to the area of concern. I definitely would not have done that if it meant putting little holes into the wall.