Embodiments provide mixing methods, systems, apparatuses, devices and assemblies that enable high-accuracy mixing of two or more substances in a manner that controls the concentrations of one or more substances in the resulting mixture. A mixing apparatus (100) may enable mixing of two or more substances at a mixing zone or conduit (112). The mixing apparatus may include one or more sensors (120) for detecting one or more characteristics of the mixture during the mixing process. The sensors may detect the mixture characteristics continuously, at intervals or as prompted by a user. The mixture characteristics may be used, in the sensors or in control circuitry, to generate an indication of the concentration of a first constituent substance in the mixture. Based on the detected concentration, the mixing apparatus may automatically adjust a supply of the first substance to the mixing zone or conduit (112).