Scale - A numerical factor which relates the measured value to the actual value.
Scale - Surface oxidation, consisting of partially adherent layers of corrosion products, left on metals by heating or casting in air or in other oxidizing atmospheres. Scale is the product of the corrosion process of steel with a porous surface layer or flake, in volume greater than the metal from which it was formed.
Loose scale - Sheets of rust falling off it the surveyor hits the structure with his test hammer. Loose scale can best be removed by hand or power tool cleaning or a combination of these.
Mill scale - Thick oxide film formed on rought-metal products which have been hotrolled or forged and allowed to cool in air.