  Measurement uncertainty plays a critical role in the process of experimental
physics. It is useful to be able to assess student proficiency around the topic
to iteratively improve instruction and student learning. For the topic of
measurement uncertainty, we developed an assessment tool called the Survey of
Physics Reasoning on Uncertainty Concepts in Experiments (SPRUCE), which aims
to assess students' knowledge, and use of, a variety of concepts related to
measurement uncertainty. This assessment includes two isomorphic questions
focused on comparing two measurements with uncertainty. One is presented
numerically and the other pictorially. Despite the questions probing identical
concepts, students answer them in different ways, indicating that they rely on
distinct modes of representation to make sense of measurement uncertainty and
comparisons. Specifically, students score much higher on the pictorially
represented item, which suggests possible instructional changes to leverage
students' use of representations while working with concepts of measurement
uncertainty.
