NCCER Millwright Practice Exam

To check an instrument for parallax, what should you do while looking at the crosshairs?

1. Adjust your position

2. Move your head slightly

3. Look from different angles

4. Close one eye

The correct answer is: Move your head slightly

To check an instrument for parallax while looking at the crosshairs, moving your head slightly is essential. Parallax occurs when the crosshairs appear to shift position relative to the measurement scale due to an angle between the observer's line of sight and the instrument's line of sight. By subtly altering your head position, you can observe whether the crosshairs maintain a consistent alignment with the scale. If the crosshairs appear to move in relation to the scale, it indicates that there is parallax present, and adjustments may need to be made to the instrument to ensure accurate readings. This technique is fundamental in precision measurements where even slight discrepancies can lead to significant errors. Adjusting your position may not adequately address parallax, as it could lead to a more significant misalignment or an incorrect line of sight. Looking from different angles may not provide the same nuanced feedback about the alignment of the crosshairs and the scale as moving your head slightly does. Closing one eye does not typically help in this situation; rather, it may create the illusion of alignment when in fact, the parallax issue could still exist.