Abstract: A retrofit device includes an elongated displacement element of uniform cross-section. When disposed in an upright position in a chamber of a multi-chamber fluid measuring device, the retrofit device reduces the volume of the chamber and thereby alters the ratio which the volume of that chamber bears to another chamber of the measuring device. The retrofit device may be advantageously employed in a syrup chamber of a multi-chamber measuring vessel used for assessing the volumetric ratio of syrup and diluent components used to prepare a beverage in a post-mix dispenser.