Inch

An inch (plural: inches; abbreviation or symbol: in or ″ – a double prime) is a unit of length in the imperial and United States customary systems of measurement. Historically an inch was also used in a number of other systems of units. Traditional standards for the exact length of an inch have varied in the past, but since July 1959 when the international yard was defined as 0.9144 metres, the international inch has been exactly 25.4 mm. There are 12 inches in a foot and 36 inches in a yard.

Usage

The inch is a commonly used customary unit of length in the United States,Canada, and the United Kingdom. For the United Kingdom, guidance on public sector use states that since 1 October 1995, without time limit, the inch (along with the foot) is to be used as a primary unit for road signs and related measurements of distance (with the possible exception of clearance heights and widths) and may continue to be used as a secondary or supplementary indication following a metric measurement for other purposes.

Inch (disambiguation)

An inch is a unit of measurement.

Inch or inches may also refer to

Units

Places

"Inch" in Scottish and Irish placenames (an anglicisation of the Gaelic innis) usually meaning an island or meadow:

Display size

On 2D displays, such as computer monitors and TVs, the display size (or viewable image size or VIS) is the physical size of the area where pictures and videos are displayed. The size of a screen is usually described by the length of its diagonal, which is the distance between opposite corners, usually in inches. It is also sometimes called the physical image size to distinguish it from the "logical image size," which describes a screen's display resolution and is measured in pixels.

Optimal screen size and viewing distance

The TV image is composed of many lines of pixels. Ideally, the TV watcher sits far enough away from the screen that the individual lines merge into one solid image. The watcher may sit even farther away and still see a good picture, but it will be a smaller portion of their visual field. The resolution of the human eye (with 20/20 vision) is about one minute of arc. For full HDTV resolution, this one minute of arc implies that the TV watcher should sit 4 times the height of the screen away. So the ideal set size can be determined from the chart below by measuring the distance from where the watcher would sit to the screen in centimeters (or inches), dividing that by 4, and comparing with the screen heights below. Do not be surprised if the observer can see the pixels at this viewing distance as most normal people see far better than 6/6 ([20/20 vision]). If the user is replacing a standard definition TV with an HDTV this implies that the best visual experience will be with a set that is twice as tall as the standard definition set. As the average size LCD TV being sold is now 38", which is only about 15% taller than a 27" standard definition TV, this means that most consumers buy HDTV sets that are smaller than what they could utilize. Cost and budget also limit screen size.

Harmonic

The term harmonic in its strictest sense describes any member of the harmonic series. The term is employed in various disciplines, including music and acoustics, electronic power transmission, radio technology, etc. It is typically applied to repeating signals, such as sinusoidal waves. A harmonic of such a wave is a wave with a frequency that is a positive integer multiple of the frequency of the original wave, known as the fundamental frequency. The original wave is also called 1st harmonic, the following harmonics are known as higher harmonics. As all harmonics are periodic at the fundamental frequency, the sum of harmonics is also periodic at that frequency. For example, if the fundamental frequency is 50 Hz, a common AC power supply frequency, the frequencies of the first three higher harmonics are 100 Hz (2nd harmonic), 150 Hz (3rd harmonic), 200 Hz (4th harmonic) and any addition of waves with these frequencies is periodic at 50 Hz.

Characteristics

Most acoustic instruments emit complex tones containing many individual partials (component simple tones or sinusoidal waves), but the untrained human ear typically does not perceive those partials as separate phenomena. Rather, a musical note is perceived as one sound, the quality or timbre of that sound being a result of the relative strengths of the individual partials.

Harmonic series (music)

A harmonic series is the sequence of sounds where the base frequency of each sound is an integral multiple of the lowest base frequency.

Pitched musical instruments are often based on an approximate harmonic oscillator such as a string or a column of air, which oscillates at numerous frequencies simultaneously. At these resonant frequencies, waves travel in both directions along the string or air column, reinforcing and canceling each other to form standing waves. Interaction with the surrounding air causes audible sound waves, which travel away from the instrument. Because of the typical spacing of the resonances, these frequencies are mostly limited to integer multiples, or harmonics, of the lowest frequency, and such multiples form the harmonic series (see harmonic series (mathematics)).

The musical pitch of a note is usually perceived as the lowest partial present (the fundamental frequency), which may be the one created by vibration over the full length of the string or air column, or a higher harmonic chosen by the player. The musical timbre of a steady tone from such an instrument is determined by the relative strengths of each harmonic.

Harmonic (mathematics)

In mathematics, a number of concepts employ the word harmonic. The similarity of this terminology to that of music is not accidental: the equations of motion of vibrating strings, drums and columns of air are given by formulas involving Laplacians; the solutions to which are given by eigenvalues corresponding to their modes of vibration. Thus, the term "harmonic" is applied when one is considering functions with sinusoidal variations, or solutions of Laplace's equation and related concepts.

See also