Metals for precision work — for high-grade measuring instruments and precision components, which steel is traditionally preferred? Select the best choice.

Introduction / Context:
Precision instruments demand stable dimensions, fine finish, and reliable mechanical properties. Historical metallurgical developments produced specialty steels tailored for gauges, measuring tools, and high-accuracy components. This question probes knowledge of such a traditional premium steel choice.

Given Data / Assumptions:

• Applications include precision gauges, micrometers, dies, and measuring rules.
• Focus on steel quality, cleanliness, and dimensional stability.
• Traditional nomenclature is used.

Concept / Approach:
Whitworth compressed steel refers to steel produced by fluid compression techniques associated with Sir Joseph Whitworth, yielding superior soundness and homogeneity for precision applications. Compared with ordinary cast or Bessemer steels, Whitworth compressed steel historically offered fewer blowholes and better uniformity—attributes critical for instruments. Mild steel lacks hardness and stability for many precision tools without subsequent alloying/heat treatment.

Step-by-Step Solution:

Verification / Alternative check:
Engineering histories and manufacturing texts cite Whitworth processes for producing high-quality steels used in gauges and precision tooling before modern vacuum and ESR routes became common.

Why Other Options Are Wrong:

• Cast steel: Generic; quality varies; often more defects than specialty routes.
• Bessemer steel: Early mass steel; impurity control less refined for precision needs.
• Mild steel: Ductile but lacks the hardness and stability for fine instruments.

Common Pitfalls:
Assuming modern alloy tool steels were always available; the question targets a classic, named steel associated with precision.

Final Answer:
Whitworth compressed steel