Learning goals: Teacher Facing 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. Full lesson plan (warm-up, activities, synthesis, cool-down prompt) from 7.4 Proportional Relationships and Percentages, Grade 7.