The goal of the present study focused on the use of eye tracking technology to investigate the relationship between reference point use and performance on an atypical number line estimation task. University students (N=53; M=20.8 years) completed 33 number line trials, a post-task questionnaire, and a brief math assessment. Patterns of error and fixation data were analyzed. The results presented show that adult participants adjust their strategies in response to the scale used and that the use of implicit reference points benefits performance for targets located above the midpoint value. In sum, the varying performance demonstrated within an adult population using an atypical scale suggests that adults use proportional reasoning strategies to estimate the location of a number.