Linear measurement scales: For a direct vernier scale, how do the graduations relate to the main scale and what direction do they increase?

Introduction / Context:
Vernier scales enhance precision by subdividing the main scale. Surveying instruments use either direct or retrograde verniers. Knowing their relative graduation direction prevents misreading lengths or angles during precise work.

Given Data / Assumptions:

• We compare the orientation of vernier graduations to the main scale.
• Definitions follow standard metrology conventions.

Concept / Approach:
In a direct vernier, the graduations increase in the same direction as those of the main scale, and the vernier’s least division is slightly smaller than the main scale’s least division so that a fixed number of vernier divisions equals a different number of main divisions. A retrograde vernier increases in the opposite direction. The direction of increase governs how readings are added or subtracted when aligning vernier and main scale marks.

Step-by-Step Solution:

Verification / Alternative check:
Examine any engineer’s vernier caliper or transit circle with a direct vernier; the numbering increases in the same sense along both scales.

Why Other Options Are Wrong:

• Opposite direction defines a retrograde vernier, not a direct one.
• Larger vernier least division would not produce vernier coincidence behavior for fine interpolation.

Common Pitfalls:
Confusing “direct” with “retrograde”; misinterpreting which side of the index line to read when scales are mirrored.

Final Answer:
Vernier graduations increase in the same direction as those of the main scale