A ferrite content measurement gauge is a device used to measure the amount of ferrite in a material. 

Ferrite is a magnetic material that is commonly found in stainless steel and other alloys. The gauge works by using magnetic induction to measure the ferrite content of a material.

Feritscopes are one type of handheld instrument that can be used to measure ferrite content quickly and non-destructively. Ferrite content is an important consideration in Stainless and Duplex Stainless Steels as it affects corrosion resistance and susceptibility to cracking.

Chemical, energy, and processing plants are often subject to heat, aggressive media and high pressure. These circumstances demand steel with high corrosion and acid resistance that are resilient even at high temperatures. 

If the ferrite content is too low, then the welded material is susceptible to hot-cracking, if the ferrite content is too high, the toughness, ductility as well as the corrosion resistance of the steel are reduced. 

For duplex steel, a ferrite deficit in the area of the weld seam results in stress corrosion cracking and reduction in strength.