If you have had any experience with traditional stud finders or the Bosch DMD4k (GMS120 predecessor) you may have found the results to be less that 100% accurate. In standard construction it probably works fine but on remodel jobs or in old homes with various materials if you are not confident in the results how useful is the tool going to be. The Bosch GMS120 ($69, Ohio Power Tool) adds new technology and additional levels of on screen accuracy that should provide more confidence that you have truly centered on the wood stud, wires, copper tube or rebar. Read this great article from Fine Homebuilding on How It Works. It really explains a lot on how this Wall Scanner operates. Also our friend Neil, from the UK based Toolstop blog, does a nice job in the video below highlighting the operations way better than we could by rambling on here.