An indirect measuring instrument is a tool that does not have its own graduated scale for direct reading of measurements. Instead, it is used to capture a dimension from a workpiece and then transfer it to a direct measuring instrument, such as a steel rule, to obtain the actual reading. Conversely, a specific measurement can be set on the indirect instrument using a steel rule, and then this dimension can be transferred to a job or workpiece.

Caliper: The Indirect Measuring Tool

A caliper is a prime example of an indirect measuring instrument. It is designed with two jaws that can be adjusted to either span an external dimension or fit into an internal dimension. Once the caliper's jaws are set to the desired size of the job, this captured dimension can be held and then measured against a steel rule to get the precise value. Similarly, a specific measurement can be set on the caliper using a steel rule, and then this setting can be used to transfer that exact dimension to a workpiece for marking, checking, or comparison. This characteristic makes the caliper highly effective for:

• Transferring external measurements.
• Transferring internal measurements.
• Comparing dimensions without needing a direct reading scale on the tool itself.

The versatility of the caliper in transferring measurements between a steel rule and a job makes it an indispensable tool in various mechanical and manufacturing fields.

Analysis of Other Instruments

Let's consider why the other options do not fit the description of an indirect measuring instrument used for transferring measurements between a steel rule and a job:

• Compass: A compass is primarily a drawing instrument used to create circles or arcs of a specific radius. While it can be set to a certain opening (a dimension), its core function is not for transferring linear measurements from a steel rule to a job or vice versa for general dimensional checking or replication in the same manner as a caliper.
• French curve: A French curve is a drafting aid used for drawing smooth, non-circular curves. It is not a measuring instrument at all; it's a template for drawing.
• Protractor: A protractor is a direct measuring instrument specifically designed to measure angles. It has its own graduated scale (usually in degrees) for direct reading and is used for angular measurements, not for transferring linear dimensions from a steel rule to a job.

Summary: Why Caliper Excels in Measurement Transfer

Based on the functions of these instruments, the caliper is uniquely suited as an indirect measuring instrument for the purpose of accurately transferring linear dimensions from a steel rule to a job and vice versa. Its design allows it to hold a specific measurement, which can then be read or applied elsewhere, fulfilling the requirement of an indirect transfer tool.