CIRCUIT NOISE LEVEL determining related maintenance or maintainability design require- ments. CIRCUIT NOISE LEVEL At any point in a transmission system, the ratio of the circuit noise at that point to some arbitrary amount of circuit noise chosen as a reference. CIRCUITRY A complex of circuits describing interconnection within or between systems. CIRCUITRY LAYER A circuitry layer is a layer of a printed wir- ing board containing conductors. It also includes both ground planes and voltage planes. CIRCUIT SIMULATOR A computer program that simulates the operation of an electronic circuit. In digital applications, it also ana- lyzes the efficiency of stimulus test patterns on itself. CIRCULARITY (ROUNDNESS) Circularity is a condition of a surface of revolution where (a) for a cylinder or cone, all points of the surface intersected by any plane perpendicular to a common axis are equidistant from that axis or (b) for a sphere, all points of