Learning about pendulums is often considered a difficult unit for students to understand. As for just one of the factors that make this unit difficult, it must be pointed out how to handle numerical processes. This research focused attention on the recognition of averaging and errors and examined the impact of handling numerical values on students' judgments of algebraic comparisons. As a result, it was revealed that direct comparison of multiple numerical values under each condition more easily led to recognition of errors than comparison of two averaged values. When averaging was not used, variation in numerical values or dispersion was easily imagined because measured values were directly compared. This led to easier recognition of errors.On the other hand, averaging means comparison of representative values of each of two conditions. Because two values were compared, dispersion of numerical values was difficult to imagine. This made recognition of errors more difficult. When averaging was not used, many students could improve their misconceptions. Recognizing their errors, students were able to make appropriate judgements.