a blender for plastic materials weighs a charge of virgin plastic pellets as they are added to a hopper , similarly weighs plastics regrind material as it is added to the hopper , calculates the weight of color material on the basis of the actual virgin material weight and the desired color percentage , calculates from the weight of color material and a calibration of a volumetric feeder the volumetric amount of color material needed and then dispenses the calculated volume of color material . the apparatus is hybrid , using weight ratio measuring devices for the primary components and a volumetric feeder for dispensing the additives .