Solution:

Because the pointer of the meter is usually a small distance above the scale of the meter, parallax error can occur when the operator attempts to read the scale line that “lines up” with the pointer. To counter this, some meters include a mirror along the markings of the principal scale. The accuracy of the reading from a mirrored scale is improved by positioning one’s head while reading the scale so that the pointer and the reflection of the pointer are aligned; at this point, the operator’s eye must be directly above the pointer and any parallax error has been minimized.