The Magnaflux MT-21 Series brings a whole new dimension to the world of thickness gages at an amazingly affordable price. Best of all, the MT-Series may be upgraded in the field, without returning the gage to the factory. The MT-21B is the basic model, which accepts all transducers and is capable of making accurate thickness readings on a variety of materials with access to only one side of the product. The M-21 model combines the popular features of the MT-21B and adds features such as, gain adjust, vibrating and illuminated alarms, and Transducer Wear Alert (Which informs the user when transducer replacement is needed). The M-21DL is the deluxe model and combines all of the features of the MT-21B and MT-21, but adds a 50,000 reading flexible datalogger, B-Scan and Echo-to-Echo.