Zenith On the International Space Station, "zenith" and "nadir" are used instead of "up" and "down", referring to directions within and around the station, relative to the earth. Zenith The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e. the direction in which gravity pulls, is toward the nadir. The zenith is the "highest" point on the celestial sphere. The word "zenith" derives from an inaccurate reading of the Arabic expression (), meaning "direction of the
Overhead (computing) generally specified using Big O Notation. This makes no comment on how long something takes to run or how much memory it uses, but how its increase depends on the size of the input. Overhead is "deliberately" not part of this calculation, since it varies from one machine to another, whereas the fundamental running time of an algorithm does not. This should be contrasted with algorithmic efficiency, which takes into account all kinds of resources – a combination (though not a trivial one) of complexity and overhead. Invoking a function introduces a small run-time overhead. Sometimes the compiler can minimize