A method by which the target of a toner concentration (TC) sensor can be set up based on the equivalent developability concept without using an expensive patch generator. First, use a black toner area coverage (BTAC) sensor to measure the relative reflectance (RR) of a 100% area coverage developed patch (ROS generated) at a series of development levels (V.sub.em or V.sub.dev) to generate a pseudo development curve and estimate V.sub.dO in real-time (V.sub.dO is the V.sub.dev level that starts to develop toner onto the photoreceptor belt.) Then, add a nominal delta V.sub.dev to V.sub.dO to get the development level (V.sub.dev) needed to generate 100% area coverage gray patch. Finally, using a BTAC sensor to measure the RR level of a 100% area coverage (AC) gray patch, move the target of the TC sensor, and converge the sensor's reading to the sensor's target continuously until the RR level of the gray patch hits the RR target (predefined) within the tolerance range. Thus, the target of the TC sensor is set for the xerographic system automatically.