What is backlash error and how can it be avoided in measuring instruments?

Backlash error is a type of instrumental error that occurs in measuring instruments, particularly those with screw gauges, micrometers, or other mechanisms involving a screw and nut. It arises due to the looseness or play between the screw and its nut. When the direction of rotation of the screw is reversed, there is a small amount of movement of the screw without a corresponding movement of the nut or the measuring scale. This results in an inaccurate reading.

To avoid backlash error:

• Always rotate the screw in one direction only when taking a measurement.
• If you overshoot the mark, do not reverse the screw. Instead, rotate it back by a significant amount and then approach the final reading again by rotating the screw in the original direction. This ensures that the screw always engages the nut from the same side, eliminating the play.