Prime (symbol) in the context of "Typesetting"

The foot (standard symbol: ft) is a unit of length in the British imperial and United States customary systems of measurement. The prime symbol, ′, is commonly used to represent the foot. In both customary and imperial units, one foot comprises 12 inches, and one yard comprises three feet. Since an international agreement in 1959, the foot is defined as equal to exactly 0.3048 meters. The most common plural of foot is feet. However, the singular form may be used like a plural when it is preceded by a number, as in "that man is six foot tall".

Historically, the "foot" was a part of many local systems of units, including the Greek, Roman, Chinese, French, and English systems. It varied in length from country to country, from city to city, and sometimes from trade to trade. Its length was usually between 250 mm (9.8 in) and 335 mm (13.2 in) and was generally, but not always, subdivided into twelve inches or 16 digits.

The inch (symbol: in or ″) is a unit of length in the British Imperial and the United States customary systems of measurement. It is equal to ⁠1/36⁠ yard or ⁠1/12⁠ of a foot. Derived from the Roman uncia ("twelfth"), the word inch is also sometimes used to translate similar units in other measurement systems, usually understood as deriving from the width of the human thumb.

Standards for the exact length of an inch have varied in the past, but since the adoption of the international yard during the 1950s and 1960s the inch has been based on the metric system and defined as exactly 25.4 mm.

YCbCr, Y′CbCr, also written as YC_BC_R or Y′C_BC_R, is a family of color spaces used as a part of the color image pipeline in digital video and photography systems. Like YP_BP_R, it is based on RGB primaries; the two are generally equivalent, but YC_BC_R is intended for digital video, while YP_BP_R is designed for use in analog systems.

Y′ is the luma component, and C_B and C_R are the blue-difference and red-difference chroma components. Luma Y′ (with prime) is distinguished from luminance Y, meaning that light intensity is nonlinearly encoded based on gamma corrected RGB primaries.