A digital hydrometer comprising: a base comprising a base housing having a base top surface; and a displacement vessel supported atop the base top surface, and having an interior, a top end, an opening to the interior at the top end, and a displacement vessel bottom end, the displacement vessel being in the form of a container configured such that the displacement vessel can hold a measured amount of liquid; wherein the digital hydrometer further comprises: a vessel lid at the top end of the displacement vessel, covering the opening, and capping the displacement vessel, the vessel lid comprising a lid aperture at its center; an inductive distance sensor mounted in or on the base housing and comprising an inductor; an output circuit contained in or on the base housing, in electrical communication with the inductive distance sensor and comprising a digital display device mounted on the base housing; and a hydrometer float comprising a stem at a top end, a bottom end, and a bulb proximal and extending from the bottom end toward the top end, the hydrometer float being configured to float in a displacement fluid in the displacement vessel, the stem having a stem diameter that is sufficiently narrow to pass through the lid aperture, the stem, in operation, passing through the lid aperture, and the lid aperture centering the hydrometer float in the displacement vessel, the hydrometer float further comprising a metal-ballast that changes the impedance provided by the inductor, the metal-ballast being positioned at a fixed distance from the bottom end and the change in impedance varying in relation to the proximity of the metal-ballast to the inductor, wherein when the displacement vessel is supported atop the base top surface, the digital hydrometer is configured such that (a) the inductor distance sensor senses an impedance based on a proximity of the metal-ballast in the displacement vessel to the inductor, (b) the output circuit generates a signal based on the impedance caused by the metal-ballast, and converts the signal into a digital value, and (c) the digital value is displayed on the digital display device of the base. a base comprising a base housing having a base top surface; and a displacement vessel supported atop the base top surface, and having an interior, a top end, an opening to the interior at the top end, and a displacement vessel bottom end, the displacement vessel being in the form of a container configured such that the displacement vessel can hold a measured amount of liquid; a vessel lid at the top end of the displacement vessel, covering the opening, and capping the displacement vessel, the vessel lid comprising a lid aperture at its center; an inductive distance sensor mounted in or on the base housing and comprising an inductor; an output circuit contained in or on the base housing, in electrical communication with the inductive distance sensor and comprising a digital display device mounted on the base housing; and a hydrometer float comprising a stem at a top end, a bottom end, and a bulb proximal and extending from the bottom end toward the top end, the hydrometer float being configured to float in a displacement fluid in the displacement vessel, the stem having a stem diameter that is sufficiently narrow to pass through the lid aperture, the stem, in operation, passing through the lid aperture, and the lid aperture centering the hydrometer float in the displacement vessel, the hydrometer float further comprising a metal-ballast that changes the impedance provided by the inductor, the metal-ballast being positioned at a fixed distance from the bottom end and the change in impedance varying in relation to the proximity of the metal-ballast to the inductor, wherein when the displacement vessel is supported atop the base top surface, the digital hydrometer is configured such that (a) the inductor distance sensor senses an impedance based on a proximity of the metal-ballast in the displacement vessel to the inductor, (b) the output circuit generates a signal based on the impedance caused by the metal-ballast, and converts the signal into a digital value, and (c) the digital value is displayed on the digital display device of the base. (a) the inductor distance sensor senses an impedance based on a proximity of the metal-ballast in the displacement vessel to the inductor, (b) the output circuit generates a signal based on the impedance caused by the metal-ballast, and converts the signal into a digital value, and (c) the digital value is displayed on the digital display device of the base.