The geomagnetic field is an important parameter in space physics. The International Geomagnetic Reference Field (IGRF) is a model of the Earth's main field. Current sources in the ionosphere, the interplanetary magnetic field, annual and diurnal variation, and other sporadic and unmodeled effects may alter the actual B field distribution. We investigate whether the model is nevertheless sufficiently accurate for computing ionospheric effects on radio frequency signals. Detailed analysis of scalar intensity is presented based on direct measurements of the magnetic field taken from UARS, SAC-C, Ørsted, and CHAMP, all satellites with magnetometers orbiting between 200 and 1000 km altitude. Our results indicate that the IGRF model is within 1% accuracy of the measured ionosphere B field, 92.80% of the time. Quality control issues associated with the scalar data are also discussed.