Mathematics for Plumbers CHAPTER 4 Reading Fractions of an Inch Reading a rule accurately and quickly requires careful attention to the markings on the scale and some practice. The lines marking the scale vary in length. The longest lines are the inch divisions. The shortest lines indicate sixteenths of an inch. Figure 4-2 gives several examples. To prevent costly errors, recheck each measure- ment before cutting materials. The reduced waste in both time and materials makes this procedure worthwhile. Reading a scale accurately to the nearest 1⁄16″ is easy if the ¼″ divisions are used as a starting point and the smaller parts of an inch are added to or subtracted from the larger divisions to get the correct reading. See Figure 4-3. This method is much faster and more accurate than attempting to count the number of spaces. Adding and Subtracting Lengths Frequently, you will need to add two lengths that are given in fractions of an inch. Figure 4-4 illustrates direct addition by putting two scales together. It also shows how to add measurements given in fractions. Subtracting dimensions given in fractions of an inch is another skill you will need. The proce- dure, shown in Figure 4-5, is nearly identical to that for addition. Note that the fractions must have common denominators before they can be subtracted. When the denominators of the fractions are not the same number, the procedure shown in Figure 4-6 must be followed. The fractions must Objectives This chapter reviews the basic mathematics likely to be needed by the plumber. After studying this chapter, you will be able to: Read a rule accurately to nearest 1⁄16″. Add and subtract fractions and whole numbers. Compute pipe offsets using the Pythagor ean theorem and trigonometric functions. Apply the formulas for finding area and volume. Explain and apply SI metric measure in finding length, area, volume, and temperature. Convert customary measure to metric measure. Plumbers need to make accurate measurements and calculations. They need to add and subtract dimensions, compute pipe offsets, and determine the volume of tanks. This chapter will provide the basic information needed to master these skills. In addition, metric measurement is introduced. Technical Terms Pythagorean theorem Trigonometric functions Laying length Plumber’s rule Measurement The basic measuring tools used by the plumber are the folding rule and the steel tape. Whichever is used, the scale printed on the tool is the same. Figure 4-1 illustrates how the basic scale is divided into parts of an inch. 71 Copyright Goodheart-Willcox Co., Inc.
Previous Page Next Page