about the size of one can be determined by measuring the size of the other, and determining the difference in weight between the two. For example, if two blocks of wood are equally dense, and it is known that one weighs ten kilograms and the other weighs twenty kilograms, and that the ten kilogram block has a volume of one cubic foot, then it can be deduced that the twenty kilogram block has a volume of two cubic feet. Conceptualization and generalization The concept of size is often applied to ideas that have no physical reality. In mathematics, magnitude is the size of a mathematical object, which is an abstract object with no concrete existence. Magnitude is a property by which the object can be compared as larger or smaller than other objects of the same kind. More formally, an object's magnitude is an ordering (or ranking) of the class of objects to which it belongs. There are various other mathematical concepts of size for sets, such as: measure (mathematics), a systematic way to assign to each suitable subset a number cardinality (equal if there is a bijection), of a set is a measure of the "number of elements of the set" for well-ordered sets: ordinal number (equal if there is an order-isomorphism) In statistics (hypothesis testing), the "size" of the test refers to the rate of false positives, denoted by α. In astronomy, the magnitude of brightness or intensity of a star is measured on a logarithmic scale. Such a scale is also used to measure the intensity of an earthquake, and this intensity is often referred to as the "size" of the event. In computing, file size is a measure of the size of a computer file, typically measured in bytes. The actual amount of disk space consumed by the file depends on the file system. The maximum file size a file system supports depends on the number of bits reserved to store size information and the total size of the file system in terms of its capacity to store bits of information. In physics, the Planck length, denoted , is a unit of length, equal to . It is a unit in the system of Planck units, developed by physicist Max Planck. The Planck length is defined in terms of three fundamental physical constants: the speed of light, the Planck constant, and the Newtonian constant of gravitation.