Introduction - Mathematics and Statistics for the Environment - page 14

From the example above, it can be seen that a conversion factor changes known quantities in one
unit of measure to an equivalent quantity in another unit of measure. In making the conversion from
one unit to another, we must know two things:

1. The exact number that relates the two units

2. Whether to multiply or divide by that number

When making conversions, confusion over whether to multiply or divide is common; on the other
hand, the number that relates the two units is usually known and thus is not a problem. Understanding
the proper methodology—the “mechanics”—to use for various operations requires practice and
common sense.
Along with using the proper mechanics (and practice and common sense) in making conversions,
probably the easiest and fastest method of converting units is to use a conversion table. The simplest
conversion requires that the measurement be multiplied or divided by a constant value. For instance,
if the depth of wet cement in a form is 0.85 ft, multiplying by 12 in. per foot converts the measured
depth to inches (10.2 in.). Likewise, if the depth of the cement in the form is measured as 16 in.,
dividing by 12 in. per ft converts the depth measurement to feet (1.33 ft).

1.4.1 W eight , C onCentration , and F loW
Using Table 1.4 to convert from one unit expression to another and vice versa is good practice; how-
ever, in making conversions to solve process computations in water treatment operations, for exam-
ple, we must be familiar with conversion calculations based upon a relationship between weight,
flow or volume, and concentration. The basic relationship is

Weight = Concentration × (Flow or Volume) × Factor (1.1)

DID YOU KNOW?

Many environmental health professionals choose to work for the Food Safety and Inspection
Service (FSIS) at the federal level or for other food inspection services at the state and local
government levels. Their objective, of course, is to ensure that meat, meat food, poultry, and
poultry food products distributed in interstate commerce or locally are wholesome, not adul-
terated, and properly marked, labeled, and packaged. One obstacle that inspection person-
nel encounter in ascertaining restricted ingredient compliance with the regulations is that
calculations for allowable ingoing amounts could be based on one of five different weights.
These different weights vary according to the type of ingredient, type of product, and reason
for using the ingredient in the product. The five weights (or bases for restricted ingredient
calculations) are

• Green weight —Weight of the meat and/or poultry byproduct (meat block) compo-
nent at formulation
• Formulated weight —Total weight after meat products are added to sausage products
at the time of formulation, excluding the water and ice
• Finished weight —Total weight of the entire meat or poultry product, including
breading and butter
• Projected finished weight —Total weight of meat or poultry, including nonfat dry
milk, soy flours, and cereals added
• Weight of the fat content —Weight of the fat content of a fresh meat or poultry product