Drawing Aids, Continued
Protractors
To use a protractor for laying off or measuring angles, follow this table:
(Continued)
Step
Action
1
Place the protractor along a straight line CA.
2
Place the O degree mark at the vertex of the desired angle.
3
Locate the desired angle (b) and its corresponding compliment (d).
4
Draw line BD.
Using four points of reference decreases the possibility of error in
measurement.
Figure 2-51 illustrates the stability of a four-point reference system.
Figure 2-51. —Protracting an angle using four-
point reference.
Continued on next page
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