Metrology: The Science of Measurement

Precision vs. Accuracy

Metrology is an activity developed by Learning Undefeated to help students understand the difference between precision and accuracy and how both play an important role in the manufacturing industry.

In this activity, students will use tools like rulers and calipers to measure items and collect class data to calculate averages and standard deviations. Students will also be introduced to the idea of tolerance in a designed part. Students will see that different tolerances are required depending on the function of the part. Interference and clearance fits will be discussed as students try to determine the best hole tolerance for a metal pin.

Learning Objectives

Students will be able to

Measure metal pins for their length and diameter using rulers and calipers.
Calculate class averages and standard deviations.
Determine fits for metal pins by testing with a tolerance block.

Standards Alignments + Connections

Texas Essential Knowledge and Skills

Principles of Manufacturing

PRINMAN.1.C: Use a variety of measuring instruments

PRINMAN.2.C: Apply mathematics concepts to solve manufacturing problems

PRINMAN.2.E: Use the appropriate units of measure

PRINMAN.7.A: Investigate an area of interest in manufacturing

PRINMAN.7.B: Analyze the various specializations in manufacturing

Diversified Manufacturing I

DIMANU1.2.A: Use tools and equipment commonly employed in manufacturing in a safe manner

Engineering Design and Problem Solving

ENGDPRS.10.A: Evaluate the readings of dial calipers and micrometers to make precise measurements

ENGDPRS.10.E: Examine the maximum and minimum limits of a dimension given its tolerance

Activity Components

Pre-Laboratory Engagement

Students should be familiar with measuring with standard 12 inch rulers (measuring in inches and centimeters) and familiar with the basics of significant figures.

We recommend using the following resource to review these topics: Using a Ruler.

Activity

In this activity, students will see hands on the difference between precision and accuracy. They will do this using a variety of measuring tools and units of measure with 3 metal dowel pins of different lengths and diameters.

In the first half of the activity, students will use the measuring tools provided to determine the length and diameter of each given metal dowel pin. Class data will be collected so the class can discuss what an average is as well as what a standard deviation is. Students will also learn the importance of tool calibration for best accuracy as they realize that the rulers provided are not actually measuring 12 inches but rather 11 inches. Students will have the opportunity to discuss the pros and cons of using English and Metric measurements and why one can be preferred over another in certain circumstances.

In the second half of the activity, students will see that small differences can lead to greatly different part functions. Students will use a tolerance block with slightly different sized holes to see that though they all look the same, the pins fit differently into each: some slide right through while others can be pushed in and hold firm. Students will make an informed decision about the size hole needed for a specific situation based on their observations.

Post-Laboratory Extension

Students can explore more precise measuring instruments like dial or vernier calipers and micrometers.

We recommend using the following resource to dive practice with these tools: The Ruler Game.

Additional Resources

Measurement and Precision Lesson Plan

This lesson challenges students to think like those who design & manufacture surgical instruments and devices by illustrating the concept of measurement and precision.

Difference Between Accuracy and Precision in Production Machining

This short article provides a thorough overview of what accuracy and precision in the machining world.

Accuracy Versus Precision: The Most Important Concept in Quality and Metrology

This short video (4:04) reviews the misconceptions about precision and accuracy as well as describing how the terms are applied in manufacturing.

Types of Fits: How to Choose a Fit for Engineering Application

This short article describes the common fits that engineers use when two components need to fit or interact with one another.