A Feritscope is an instrument used for non-destructive testing to measure the ferrite content in austenitic and duplex stainless steel. It uses magnetic induction to determine the ferrite content, which is crucial for ensuring the desired mechanical and corrosion resistance properties of these materials, especially in welded applications. The Feritscope can be used to assess weld seams, ensure proper ferrite content in duplex stainless steel (ideally around 50%), and identify potential issues like ferrite deficit or excess.