Optical Square – Correct Hand Position for Offsets on Right Side of Chain Line When taking offsets with an optical square on the right-hand side of the chain line, how should the instrument be held to observe a right angle correctly?

Introduction / Context:
Optical squares are used in chain surveying to set out or check right-angled offsets quickly. Because the field of view and mirror orientation are fixed relative to the casing, the way you hold the instrument depends on which side of the chain you are observing, ensuring the reflected and direct images coincide correctly at 90 degrees.

Given Data / Assumptions:

• Offset required on the right-hand side of the chain line.
• Standard optical square with fixed mirror arrangement.
• Observer stands on or near the chain line.

Concept / Approach:

For offsets to the right, the optical square is typically held in the right hand, upright, so that the direct image of the ranging rod on the chain line and the reflected image of the offset point align at the etched line when a right angle is achieved. Reversing hand or inverting the instrument causes awkward viewing geometry and possible misreadings in routine practice.

Step-by-Step Solution:

Verification / Alternative check:

Field manuals depict right-hand/upright for right-side offsets and left-hand/upright for left-side offsets, keeping the instrument orientation consistent with the side of observation.

Why Other Options Are Wrong:

Upside-down holding changes reference lines; left-hand for right-side offsets complicates alignment; claiming orientation does not matter ignores the optical design.

Common Pitfalls:

Tilting the instrument, introducing parallax; standing off the chain line; confusing right vs left arrangement.

Final Answer:

By the right hand, held upright