Simple Survey Tools – Primary Use of a Cross-Staff in Chain Surveying In chain and offset surveying, the basic cross-staff is primarily used for which operation on the ground?

Introduction:
A cross-staff is a simple optical square used in basic surveying to project perpendiculars from a baseline. It is light, inexpensive, and quick to use for setting offsets to locate details such as fences, buildings, and hedges.

Given Data / Assumptions:

• Survey context: chain and tape measurements of a baseline.
• Need to locate features by perpendicular offsets to the baseline.
• Tool: cross-staff or optical square with right-angle sighting slots or prisms.

Concept / Approach:

By aligning one slit with the chain line and turning the instrument until the other slit sights the object, the cross-staff ensures a right angle between the baseline and the offset line. Offsets are then measured with tape along the perpendicular to plot features accurately on the plan.

Step-by-Step Solution:

Verification / Alternative check:

Where higher precision is required, an optical square provides the same 90° function with better optics but the principle remains identical.

Why Other Options Are Wrong:

Cross-staff does not measure gradients (clinometers are used), cannot take levels like a dumpy level, and does not measure long distances by itself.

Common Pitfalls:

Using the cross-staff off the chain line; neglecting to check instrument orientation causing skewed offsets.

Final Answer:

Setting out right angles to establish offsets from a chain line