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It comes from the definition of the ampere. The current definition of the ampere is based on a formula that involves the permeability of free space. Because the result of that formula is defined to be a fixed number (2 x 10-7 Newtons, in order to define the amp), it makes the permeability of free space a fixed number as well. The 4 pi comes ...
Measure for how easily current flows through a material siemens (S = Ω −1) L −2 M −1 T 3 I 2: scalar Electrical conductivity: σ: Measure of a material's ability to conduct an electric current S/m L −3 M −1 T 3 I 2: scalar Electric potential: φ: Energy required to move a unit charge through an electric field from a reference point ...
A mathematical constant is a key number whose value is fixed by an unambiguous definition, often referred to by a symbol (e.g., an alphabet letter), or by mathematicians' names to facilitate using it across multiple mathematical problems. [1]
A reference dimension is a dimension on an engineering drawing provided for information only. [1] Reference dimensions are provided for a variety of reasons and are often an accumulation of other dimensions that are defined elsewhere [2] (e.g. on the drawing or other related documentation). These dimensions may also be used for convenience to ...
A ruler used as a fiducial marker. A fiducial marker or fiducial is an object placed in the field of view of an image for use as a point of reference or a measure. It may be either something placed into or on the imaging subject, or a mark or set of marks in the reticle of an optical instrument.
A scale ruler is a tool for measuring lengths and transferring measurements at a fixed ratio of length; two common examples are an architect's scale and engineer's scale.In scientific and engineering terminology, a device to measure linear distance and create proportional linear measurements is called a scale.
4Pi may refer to: IBM System/4 Pi, a family of avionics computers; 4Pi microscope, a microscope that uses interference and fluorescence computers;
A standard ruler is an astronomical object for which the actual physical size is known. By measuring its angular size in the sky, one can use simple trigonometry to determine its distance from Earth. In simple terms, this is because objects of a fixed size appear smaller the further away they are.