  Models of physical systems are used to explain and predict experimental
results and observations. When students encounter discrepancies between the
actual and expected behavior of a system, they revise their models to include
the newly acquired observations, or change their apparatus to better represent
their models. The Modeling Framework for Experimental Physics describes the
process of matching measurements and observations to models by making revisions
to resolve discrepancies. As part of a larger effort to create assessments of
students' modeling abilities in the context of upper-division electronics
courses, we used the Modeling Framework to develop and code think-aloud
problem-solving activities centered on troubleshooting an inverting amplifier
circuit. We observed that some participants iteratively and continuously made
measurements and revisions if they could not immediately propose a cause for an
observed discrepancy. This pathway has not been previously discussed in the
Modeling Framework. In this paper, we discuss two episodes where students
undergo this process to converge on a proposed cause post hoc. We conclude by
discussing implications for a modeling assessment based on the observed
modeling behavior.
