A sensor module is able to sense at least one aspect of objects produced by a plurality of object sources. Since one sensor module or set of sensor elements is used to examine output from the plurality of object sources, sensor to sensor variation is removed as a source of error. In a multi-engine document processor, information from the sensor module is used to adjust process actuators, adjust image data and/or generate scheduling constraints to improve output consistency. For example, facing pages of a document are rendered only on marking engines operating within a predetermined tolerance of one another. Image data may be altered so that related images are within the measured capabilities of a plurality of marking engines. System actuators, such as xerographic actuators, of selected marking engines are adjusted to improve output consistency between marking engines.