We have examined 204 bow shock crossings observed in the magnetic field and plasma data on ISEE 1. Using the measured upstream field and plasma data, we calculated the downstream field magnitudes by using the single-fluid MHD Rankine-Hugoniot jump conditions, and we compared the results with the observed downstream field magnitudes. We find that the simple MHD model approach can predict the downstream field magnitude only on the average, but does so quite well if (1) a polytropic index of approximately (5)/(3) is used in the calculations; (2) the angle between the upstream field and the shock normal is greater than 45¿; and (3) the Alfv¿n Mach (Ma) number is less than about 10. For angles less than 45¿ the predictions overestimate the observed field strength. For Ma>10 the predictions underestimate the observations.