Surveying hand instrument – clinometer: A clinometer (Abney level/hand level variants) is primarily used for which field task?

Introduction / Context:
A clinometer is a simple, portable instrument for quickly measuring vertical angles or gradients. It is widely used in reconnaissance surveys, forestry, road alignment checks, and slope staking where a full theodolite is unnecessary. The question asks for its primary function in the field.

Given Data / Assumptions:

• Clinometers may have bubble levels and protractor scales.
• Some variants incorporate a small telescope (Abney level) and stadia scale.
• Readings yield angle of elevation, depression, or percent grade directly.

Concept / Approach:
By sighting a target with the clinometer and aligning the bubble, the user reads the vertical angle from the scale. This angle can be converted to slope ratio or percentage if required. The instrument is not designed to set right angles (a task for optical squares) or to correct instrument collimation; nor does it replace cartographic symbolization of features.

Step-by-Step Solution:

Verification / Alternative check:
Standard field procedures use clinometers for quick checks of embankment side slopes, road grades, and tree heights via simple trigonometric relationships.

Why Other Options Are Wrong:

• Correcting line of collimation requires instrument adjustments/tests (e.g., two-peg test) on levels and theodolites, not a clinometer.
• Setting out right angles uses a cross-staff or optical square.
• Defining natural features refers to mapping/cartography, not angle measurement.

Common Pitfalls:
Ignoring parallax by not focusing on the scale; reading without properly centering the bubble; using clinometer readings as precise as a theodolite without considering its lower accuracy.

Final Answer:
Measuring the angle of slope (angle of elevation or depression)