Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. Chapter 5 Measurement 73 5.2.1 US Customary In the US Customary system, linear measurement is based on the inch (in), which can be broken into fractions for precise measurement accuracy. Fractions of an Inch 0 1/8 3/8 1/4 3/4 1/2 5/8 7/8 1 1/32 3/32 1/16 3/16 5/16 7/16 9/16 11/16 13/16 15/16 5/32 7/32 9/32 11/32 13/32 15/32 17/32 19/32 21/32 23/32 25/32 27/32 29/32 31/32 Goodheart-Willcox Publisher *Note: Enlarged for visual ease. Not shown to scale. In this system, a length of 12 inches is called a foot (ft), and a length of 3 feet is known as a yard (yd). Symbols are often used to denote inches and feet. The symbol for inches is ″, while ′ is the symbol for feet. A length of 6 feet and 8 inches is written as 6′-8″. Linear Measurement−US Customary Units 0 1 0 1 2 3 4 5 6 7 8 12 inches = 1 foot 9 10 11 12 feet inches 2 24 3 36 3 feet = 1 yyard Goodheart-Willcox Publisher Typically, field measurements use inches and fractions of inches for ductwork design and construction, feet and inches for measuring piping, and feet for calculating air volume and movement. Yards are seldom used in HVACR linear measurement. 5.2.2 SI SI linear measurement is based on the meter (m), which is spelled metre in all English-speaking countries except the United States. The method for determining the length of the meter has changed over the past few centuries, but it has now been standardized and accepted throughout the world. The SI or metric system works on the decimal system. Thus, powers of ten are used to identify lengths that are shorter and longer than the meter. For example, 1/1000 of a meter is called a millimeter (mm), while 1000 meters is called a kilometer (km). Linear Measurement−SI Units 0 1 .1 2 .2 3 .3 0 100 10 1000 2 4 6 8 10 20 30 10 1 100 1 3 5 7 9 10 centimeters = 1 decimeter 10 mm = 1 cm centimeters decimeters millimeters 10 decimeters = 1 meter Goodheart-Willcox Publisher *Note: Enlarged for visual ease. Not shown to scale. 5