Parallax Error in Analog Measurements

Steps:

• Parallax error occurs when the observer's eye is not perpendicular to the scale, causing misreading.
• Identify methods: Assume 1 uses a digital display (no parallax), 2 uses a ruler or vernier scale (prone to parallax), 3 uses a graduated cylinder for volume (eye-level alignment needed).
• Eliminate methods without line-of-sight alignment issues.
• Select options where only 2 and 3 qualify.

Why D is correct:

• Parallax affects analog linear scales in methods 2 and 3, per the definition of observer-scale misalignment.

Why the others are wrong:

• A includes 1, which lacks a physical scale for parallax.
• B excludes 3, a common parallax-prone volume measurement.
• C excludes 2, a standard linear measurement with parallax risk.

Final answer: D