Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. Chapter 5 Measurement 75 5.3.2 SI SI capacity measurement is based on the liter (l). The milliliter (ml) is 1/1000 of a liter, and the kiloliter is 1000 liters. Like the linear measurements in SI, the capacity measurements work on the decimal system and use prefixes added to fi liter. 5.4 Weight Measurement Weight and mass are commonly confused terms. Though they are not the same thing, the terms are often used interchangeably in the HVACR field. Mass may be defi as the amount of something’s matter, while fined weight expresses the value of the gravitational force exerted on the matter. In other words, mass is constant, but weight depends on the force of gravity on a mass. This text will use the term weight rather than mass. 5.4.1 US Customary In the US Customary system, weight is measured in pounds (lb) and ounces (oz). An ounce is 1/16 of a pound, and a ton (t) is defi as 2,000 pounds. When fined measuring the moisture content of air, the grain (gr) is used. A grain is 1/7,000 of a pound. The grain is also used in water chemistry for boilers and cooling systems as a unit of measurement for mineral content in water. In that context, one grain equals 17.1 parts per million (ppm) of hardness. 1 ounce 1 ounce 1 ounce 1 ounce 1 ounce 1 ounce 1 ounce 1 ounce 1 ounce 1 o nce 1 ounce 1 ounce 1 ounce 1 ounce 1 ounce Weight Measurements in US Customary Units 1 pound 16 ounces (oz) = 1 pound (lb) 2,000 pounds = 1 ton Goodheart-Willcox Publisher 5.4.2 SI The kilogram (kg) is the base unit of weight measurement in SI units. It is equal to 1000 grams. The gram (g) is 1/1000 of a kilogram. For measuring the moisture content of air, the unit of measurement is milligrams per cubic meter (mg/m3). 5