Table 1. Converting between feet and inches.
| Feet | Inches |
| 5.00 | 60 |
| 6.25 | 75 |
| 5.50 | 66 |
| 5.75 | 69 |
Some conversions require that you multiply by a number and then add a second number. A good example of this is the transformation between degrees Centigrade and degrees Fahrenheit. Table 2 shows the temperatures of 5 US cities in the early afternoon of November 16, 2002.
Table 2. Temperatures in 5 cities on 11/16/2002.
| City | Degrees Fahrenheit | Degrees Centigrade |
| Houston | 54 | 12.22 |
| Chicago | 37 | 2.78 |
| Minneapolis | 31 | -0.56 |
| Miami | 78 | 25.56 |
| Phoenix | 70 | 21.11 |
The formula to transform Centigrade to Fahrenheit is:
The formula for converting from Fahrenheit to Centigrade is
The transformation consists of multiplying by a constant and then adding a second constant. For the conversion from Centigrade to Fahrenheit, the first constant is 1.8 and the second is 32.
Figure 1 shows a plot of degrees Centigrade as a function of degrees
Fahrenheit. Notice that the points form a straight line. This will always be the case if the transformation from one scale to another consists of multiplying by one constant and then adding a second constant. Such transformations are therefore called linear transformations.
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