Dimensional metrology — the most appropriate standard used to check and calibrate the accuracy of micrometers, vernier calipers, and dial indicators in a workshop or lab setting is:

Introduction / Context:
Measuring instruments such as micrometers, vernier calipers, and dial indicators must be verified against traceable standards to ensure accuracy. The choice of verification artifact depends on whether you are checking linear displacement, hole sizes, shaft sizes, or clearances. This question focuses on the most universal standard for linear dimension verification and calibration.

Given Data / Assumptions:

• Instruments: outside micrometers, vernier calipers, dial indicators (linear displacement).
• Need: precise, traceable lengths to build up various target dimensions.
• Environment: workshop or metrology lab with basic calibration setup.

Concept / Approach:

Slip gauges (gauge blocks) are precision lapped blocks of known lengths that can be wrung together to create a wide range of exact reference dimensions. They provide traceability to national or international standards and are ideal for checking the linear accuracy and zero error of comparative instruments. By contrast, ring and plug gauges verify cylindrical sizes at fixed dimensions only, and feeler gauges are thin leaves used for gap or clearance, not for full-scale linear calibration.

Step-by-Step Solution:

Verification / Alternative check:

Calibration procedures typically specify combinations of slip gauges to span the instrument range, checking at multiple points for linearity, repeatability, and zero setting. This practice is widely documented in metrology handbooks and ISO standards on length measurement.

Why Other Options Are Wrong:

Feeler gauge — Suitable for clearance checks, not precision calibration over a range.
Ring gauge — Valid for checking external diameters at one size; not general linear calibration.
Plug gauge — Valid for internal diameters; again a fixed-size check, not a buildable linear standard.

Common Pitfalls:

Using a single ring or plug gauge to infer general instrument accuracy; failing to check multiple points across the measurement span with slip gauges.

Final Answer:

slip gauge