AUDIT TRAIL A-STAGE An early stage in the reaction of thermosetting resins in which the material is still soluble in certain liquids and may be liq- uid or capable or becoming liquid upon heating. ATOMIC HYDROGEN WELDING An arc welding process that produces coalescence of metals by heating them with an electric arc maintained between two metal electrodes in an atmosphere of hydrogen. Shielding is obtained from the hydrogen. Pressure may or may not be used, and filler metal may or may not be used. ATTACHMENT A basic part, subassembly, or assembly designed for use in conjunction with another assembly, unit, or set, contribut- ing to the effectiveness thereof by extending or varying the basic function of the assembly, unit, or set. ATTENUATION A general term used to denote a decrease in mag- nitude (of power or field strength) in transmission from one point to another. It may be expressed as a ratio or, by extension of the term, in decibels. ATTRIBUTE (1) A characteristic or property that is appraised in