The Magnetospheric Specification Model (MSM) calculates electron and ion fluxes that may endanger spacecraft. This thesis is to evaluate the electron flux levels specified by the MSM by comparison with the Garrett model output and spacecraft observations for the large magnetic storm of April 1988. The MSM is a magnetospheric physics model which uses ground-based and satellite data as input. The Garrett model, on the other hand, is a statistical model based on average geosynchronous electron fluxes. The MSM flux enhancement predictions are in better temporal agreement than the other model. The largest error of the MSM is associated with flux dropouts which are observed by the spacecraft but not predicted by the MSM. The other possible error sources are (1) the MSM does not properly represent extreme thinning of the plasma sheet, (2) the MSM tends to overestimate the convection electric field.