Question

How to avoid parallax error when reading a scale?

Has to be something other than reading at eye level because my teacher said that is too generic

Answer 1

Here is what I think

Explanation:

Due to the thickness of the ruler used the inclined placement of eye during measurement as shown in Fig- I causes parallax error. The exact value of 4.8 cm ( when viewed vertically) changes due to inclined orientation as for example 4.6 cm and 5.0 cm in two wrongly viewed positions.

In Fig - II the ruler is placed vertical to the surface on which the line to be measured is drawn. Here thickness is avoided and that is why the reading of the ruler does not change with the change in line of view as shown in Fig - II

So to avoid parallax error
1. the line of view should be vertical marked in red dotted line in Fig - I
2. we are to make the thickness of the ruler negligible or we are to place ruler vertically on the surface on which the line to be measured is drawn.