An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ — a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. Its size can vary from system to system. There are 36 inches in a yard and 12 inches in a foot. A corresponding unit of area is the square inch and a corresponding unit of volume is the cubic inch.
The inch is one of the dominant units of measurement in the United States, and is commonly used in Canada. In the US and commonly in the UK, Canada and Ireland, personal heights are expressed in feet and inches by people of all ages, and as of 2008 by people over the age of about 40 in Australia. In Australia, Canada and New Zealand, personal heights are shown in metric units on official documents. In engineering fields, both are used - for example in engine reconditioning, the unit of measurement, and dimensions used would follow that under which the component/engine was manufactured.
Before the introduction of the metric system of units, many European countries used equivalents to the inch as a unit of length measurement; for instance the French Pouce and the German Zoll.
International inch
In 1959 the United States and countries of the Commonwealth of Nations defined the length of the international yard to be exactly 0.9144 meters. Consequently, the international inch is defined to be exactly 25.4 millimeters.
The international standard symbol for inch is in (see ISO 31-1, Annex A). In some cases, the inch is denoted by a double prime, which is often approximated by double quotes, and the foot by a prime, which is often approximated by an apostrophe. For example, 6 feet 4 inches is denoted as 6′4″ (or approximated as 6'4").
What is a Centimeter?
(from Wikipedia)
A centimetre (American spelling: centimeter, symbol cm) is a unit of length in the metric system, equal to one hundredth of a metre, which is the current SI base unit of length. Centi is the SI prefix for a factor of 10 − 2.] Hence a centimetre can be written as 10×10 − 3 m (engineering notation) or 1 E-2 m (scientific E notation) — meaning 10 × 1 mm or 1 m / 100 respectively. The centimetre is the base unit of length in the now deprecated centimetre-gram-second system of units.
Though for many physical quantities, SI prefixes for factors of 103 - like milli and kilo - are often preferred by technicians, the centimetre remains a practical unit of length for many everyday measurements. A centimetre is approximately the width of the fingernail of an adult person.
