Abstract: A liquid mixing system for preparing batches of liquids including paints and dyes in a mixing vessel provided with agitation means; delivery of mixing constituents to the mixing vessel being computer controlled and effected by positive displacement pumps transferring liquids from individual supply conduits and reservoirs via spring loaded single action check valves; the amount of constituent added to the mixing vessel being metered by the computer on the basis of constituent liquid weight monitored by a load cell at the mixing vessel; the delivery of constituent liquid to the mixing vessel under the control of the computer becoming incremental after delivery of a percentage between 80-99.9% of the target weight to the mixing vessel in order that the precise target weight be achieved.