SCRATCH acceptability of the lot or batch (acceptance and rejection num- bers). SANDWICH CONSTRUCTION A structural panel concept con- sisting, in its simplest form, of two relatively thin, parallel sheets of structural material bonded to, and separated by, a relatively thick, lightweight core. SATURATION (1) An equilibrium condition in which the net rate of absorption under prescribed conditions falls essentially to zero. (2) In a communication system, that condition wherein a compo- nent of the system has just reached its maximum traffic-handling capacity. (3) That point at which the output of a linear device devi- ates significantly from being a linear function of the input when the input signal is increased. SCALING A formation at high temperature of thick corrosion product layers on a metal surface, or the deposition of water-insol- uble constituents on a metal surface. SCAN RATE The process of examining an area, a region in space,