1. A method for determining wafer bias, the method comprising: detecting output of a generator to identify a generator output complex voltage and current, the generator coupled to an impedance matching circuit, the impedance matching circuit coupled via a radio frequency (RF) transmission line to an electrostatic chuck (ESC) of a plasma chamber; determining from the generator output complex voltage and current a projected complex voltage and current at a point along a path between an output of a model of the impedance matching circuit and a model of the ESC, the determining of the projected complex voltage and current performed using a model for at least part of the path, the model for at least part of the path characterizing physical components along the path; and applying the projected complex voltage and current as an input to a function to map the projected complex voltage and current to a wafer bias value at the ESC model.