Surveying instruments: The material used for precision leveling staffs to minimize thermal expansion errors is

Introduction / Context:
Accurate leveling demands scale stability with temperature changes. Thermal expansion of the staff material directly affects reading accuracy, especially over long runs and varying site temperatures.

Given Data / Assumptions:

• We are addressing high-precision (survey-grade) staffs.
• Temperature swings can be significant outdoors.
• The best material offers very low coefficient of thermal expansion.

Concept / Approach:
Invar (an iron–nickel alloy, ~36% Ni) is renowned for its exceptionally low thermal expansion, an order of magnitude lower than common steels. This property makes the scale length stable against temperature changes, ensuring consistent readings.

Step-by-Step Solution:
List candidates and expansion: carbon/stainless steels expand more; aluminium expands much more.Compare with invar: invar's expansion is minimal, reducing measurement drift.Select invar for precision staffs and tapes (also used in precision instruments).

Verification / Alternative check:
Instrument specifications commonly cite invar for high-accuracy tapes and staffs due to thermal stability.

Why Other Options Are Wrong:
Titanium/carbon/stainless steels expand more than invar; aluminium expands far more.

Common Pitfalls:
Selecting light materials (aluminium) for convenience while overlooking thermal stability in precision work.

Final Answer:
Invar