IT:Units of measurement
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Length
Absolute measures
A point is a unit of measurement in typography, used for measuring font sizes. In the context of a computer, the standard is the PostScript point, and there are 72 points to the inch.
A twip is a twentieth of an imperial point. So there are 20 twips per point, and 1440 twips per inch.
Other terms: A pica is equal to 12 points, so there are 6 picas to the inch.
Relative to screen
A pixel is the size of the smallest element of individual colouring on a screen. The number of pixels on a screen is defined by the screen resolution (for example a screen with a resolution of 1280 by 800 has a width of 1280 pixels and a height of 800 pixels).
So a pixel is relative in size to the screen size and screen resolution. To convert between this and twips (an absolute measure), various applications includes the functions TwipsPerPixelX (for horizontal measurements) and TwipsPerPixelY (for vertical measurements). See the following websites for examples of the implementation for different applications:
Relative to font
An em is a unit of measurement in typography, used to measure length in terms of a font. One em is equal to the point size of the font. So for a 12 point font, 1 em is equal to 12 points.
Other terms: An en is half of an em.
