An apparatus and method is disclosed for automatically controlling single-input-multi-output (SIMO) systems or processes. The control output signals of a plurality of single-input-single-output (SISO) automatic controllers are combined by a combined output setter so that these SISO controllers are converted to a multi-input-single-output (MISO) automatic controller based on certain criteria; and its resulting controller output signal is able to manipulate only one actuator to control a plurality of continuous process variables or attempt to minimize a plurality of error signals between the setpoints and their corresponding process variables. Without the need of building process mathematical models, this inventive apparatus and method is useful for automatically controlling unevenly paired multivariable systems or processes where there are less system inputs than outputs including but not limited to industrial furnaces, rapid thermal processing (RTP) chambers, chemical mechanical planarization (CMP) systems, and distillation columns.