Question

What do you mean by backlash error? How is it avoided?

ICSE Class 9 Physics Chapter Measurements and Experimentation

Answer 1

Sometimes due to wear and tear of threads of screw, it is observed that on reversing the direction of rotation of the thimble, the top of the screw does not start moving in the opposite direction at once, but it remains stationary for a part of rotation. This causes error in the observation which is called the backlash error.
To avoid backlash error, while taking the measurements, the screw should be rotated in one direction only. If it is required to change the direction of rotation of the screw, do not change the direction of rotation at once. Move the screw still further, stop there for a while and then rotate it in the reverse direction