Now consider Figure 5–5(b). [Part (a) has been repeated from Figure
5–4(b) for reference.] Here, we have placed the plus sign at point b,
meaning that you are looking at the voltage at b with respect to a. Since
point b is 6 V negative with respect to point a, V will have a value of
minus 6 volts, i.e., V 6 volts. Note also that the meter indicates 6
volts since we have reversed its leads and the red lead is now at point b
and the black at point a. It is important to realize here that the voltage
across R has not changed. What has changed is how we are looking at it
and how we have connected the meter to measure it. Thus, since the
actual voltage is the same in both cases, (a) and (b) are equivalent representations