Unit 4, Lesson 13
Measurement Error
Grade 7
Preparation
Lesson Narrative
In this lesson, students express measurement error as a percentage of the correct amount. Measurement error is the positive difference between a measured amount and the actual amount. Students see how measurement error can arise in two different ways: from the level of precision in the measurement device and from human error.
The Warm-up has students measure line segments with two different rulers, one marked in centimeters and one marked in millimeters, to introduce the concept of measurement error. The next activity introduces the convention of expressing measurement error as a percentage of the correct value. The last activity brings these two ideas together as students measure items around the classroom with the two rulers from the Warm-up and calculate the percent error.
Students engage in an important aspect of mathematical modeling as they make simplifying assumptions and approximations of a real situation (MP4).
- Compare and contrast (orally) multiple measurements of the same length that result from using rulers with different levels of precision.
- Describe (orally) possible sources of “measurement error” when measuring lengths.
- Generalize a process for calculating measurement error and expressing it as a percentage of the actual length.
Let’s use percentages to describe how accurately we can measure.
Required Preparation
The “Measuring to the Nearest” blackline master contains two versions of a centimeter ruler that students will use to measure things, so card stock would be preferable if available. In the instructions, students are told to cut out the rulers they will use from the blackline master, but to save class time, this may be done for them ahead of time. These same rulers are also used in the “Measuring Your Classroom” activity in this lesson, so they should be used carefully during the Warm-up.
Measure the height or length of several objects in your classroom to the nearest tenth of a centimeter. If possible, have at least one object per student in the class so that students don’t have to wait too long to measure things. Most of the items should be greater than 20 centimeters in length, but some can be less than or equal to 20 centimeters in length. Examples of such objects might be the width of the door, the length of the stick that holds a flag, the length of an eraser, or a side of a table or desk top.