The deviation of an alias’s path from a path of constant decl. In this example, CHORD is pointed at a high 70° decl., and there is a source at that same decl. The position of the first northern alias is shown with a dashed line. In this tangent-plane projection, the alias follows a path that is a constant vertical offset from the true source path. In contrast, a real source would follow a constant-decl. path, shown with a dotted line. These paths diverge slightly at large HAs.