12.2.2.3-4 Design of Position Indication

Alignment marks should be located to minimize parallax error.

Additional Information:
Parallax refers to the apparent change in the relative positions of objects depending on the position of the viewer. Error will be minimized if the distance between the indicator and the marks against which it is to be read is small, and if the indicator is located so that it can be viewed "straight-on," i.e., with the observer's LOS perpendicular to the plane of the alignment marks.