A consumable supply item for an imaging device holds an initial or refillable volume of fluid. Its housing defines an interior having a pair of opposed electrodes. The electrodes define a capacitance that varies in response to an amount of liquid between them. A volume space filled by the liquid varies along a length of the electrodes. The design facilitates abrupt changes in capacitance values at each change in the volume space. Devices can recalibrate fluid levels at these changes. Electrode interior surfaces face one another. At least one electrode has an open region, such as a hole or a cutout of material. In another design, a support material connects to each electrode to provide mechanical stability and create a region preventing filling by the liquid. Further embodiments contemplate material selection, construction, and modularity, to name a few.