Addition of liquid charge control agents to toner in toner development stations of electrographic reproduction apparatus

Controlling the charge on toner in a development station of an electrographic reproduction apparatus, wherein data relative to latent image charge carrying member voltage and image density control patches are sensed and development potential to achieve an aim density is calculated therefrom. A delta from an optimum development potential range is calculated, and in response to the determined delta, an amount of liquid charge control agent, from a supply of suitable liquid charge control agent, necessary to be added to the developer material in the development station to bring the toner to substantially a charge level that will enable a desired optimum developer potential is calculated. The calculated amount of liquid charge control agent is then injected directly into the development station.