Potential Definitions Since the definition of the kilogram was based on an object, the mass of a kilogram was not strictly constant. To address this problem, several approaches were pursued to redefine the kilogram. The two main approaches were the Kibble balance and the Avogadro Project. The Kibble balance uses electromagnetic force (which can be very accurately measured) to determine the weight of the object. Then, with the help of a gravimeter to accurately measure the local gravitational acceleration, the mass of the object can be determined with very high accuracy[11]. Kibble balance at the National Institute of Standards and Technology[11]. The Avogadro Project takes an independent approach. Since the kilogram and the number of silicon atoms in one mole are related by the molar mass of silicon and Avogadro's number, the kilogram can be determined by the mass of a known number of silicon atoms. Using the known spacing of atoms in a silicon lattice, the volume of a silicon sphere can be measured to determine the number of atoms in that sphere. With high enough accuracy in measuring the volume of the silicon sphere and the spacing of the atoms in the silicon lattice, the kilogram can be defined with great accuracy[12]. Achim Leistner of the Avogadro Project holds a 1 kg silicon sphere that is one of the roundest objects on Earth[12]. However different they are, these approaches are nonetheless complementary. With two independent measurements of the same quantity, we can be sure about the theory behind each approach. The two methods eventually agreed to seven decimal places[13], confirming each other's accuracy. The next year, the kilogram was redefined in terms of fundamental constants. Index Title Page 1, Mass Basics [1] 2, Old Definitions of the Kilogram [2] 3, Potential Definitions [3] 4, Current Definition Bibliography