1-45
Parallax can be a problem when you are reading a meter. Since the pointer is slightly above the scale
(to allow the pointer to move freely), you must look straight at the pointer to have a correct meter reading.
In other words, you must be in line with the pointer and the scale. Figure 1-41 shows the effect of parallax
error.
Figure 1-41.—A parallax error in a meter reading.
Figure 1-41 (A) shows a meter viewed correctly. The meter reading is 5 units. Figure 1-41(B) shows
the same meter as it would appear if you were to look at it from the right. The correct reading (5) appears
to the right of the pointer because of parallax.
The mirror on the scale of a meter, shown in figure 1-39, helps get rid of parallax error. If there is
any parallax, you will be able to see the image of the pointer in the mirror. If you are looking at the meter
correctly (no parallax error) you will not be able to see the image of the pointer in the mirror because the
image will be directly behind the pointer. Figure 1-42 shows how a mirror added to the meter in figure
1-41 shows parallax error. Figure 1-42(A) is a meter with an indication of 5 units. There is no parallax
error in this reading and no image of the pointer is seen in the mirror. Figure 1-42(B) shows the same
meter as viewed from the right. The parallax error is shown and the image of the pointer is shown in the
mirror.
