We use a data set consisting of periods for which the transpolar ionospheric potential (Φ$mathsf{pc}$) is well-determined by Super Dual Auroral Radar Network (SuperDARN) data to test the Hill model. The Hill model, as formulated by Siscoe et al. <2002>, specifies Φ$mathsf{pc}$ as a function of solar wind speed and ram pressure, the interplanetary magnetic field, the reconnection electric field (E$mathsf{r}$), and the ionospheric conductance (Σ). The periods used in our study were identified as times when the interplanetary electric field was quasi-stable for and SuperDARN coverage was sufficient to determine Φ$mathsf{pc}$. SuperDARN-determined Φ$mathsf{pc}$ (Φ$mathsf{pc}$$mathsf{SD}$) is compared to Φ$mathsf{pc}$ determined using the Hill model (Φ$mathsf{pc}$$mathsf{Hill}$) for 1317 10-min periods. A minimum in the root-mean-square difference between Φ$mathsf{pc}$$mathsf{SD}$(E$mathsf{r}$) and Φ$mathsf{pc}$$mathsf{Hill}$(E$mathsf{r}$) is achieved when Σ = 23 S and a constant potential, Φ0 = 17 kV, are used. Some aspects of the data agree very well for these values of Σ and Φ0, including the mean value of Φ$mathsf{pc}$(E$mathsf{r}$) and that both data sets clearly indicate saturation at highervalues of E$mathsf{r}$. The ram pressure dependence of Φ$mathsf{pc}$$mathsf{Hill}$, however, is inconsistent with that of Φ$mathsf{pc}$$mathsf{SD}$ and suggests that Σ should be lower than 23 S. There is also significantly more variability in Φ$mathsf{pc}$$mathsf{SD}$ for all values of E$mathsf{r}$ than the Hill model predicts.