A detailed analysis of the Gulf Stream at its separation point from the continental slope serves as a case study for interpreting EM measurements, including the incorporation of geophysical knowledge of the sediment. In addition, the first order approximation is tested by the many features at this location that contradict the approximation鈥檚 underlying assumptions: sharp horizontal velocity gradients, steep topography, and thick and inhomogeneous sediments. Numerical modeling of this location shows that the first order assumption is accurate to a few percent (a few cm sup>鈭?up>) in almost all cases. The errors in depth-varying velocity are <3%(1-3 cm sup>鈭?up>), are substantiated by the direct observations, and can be corrected by iterative methods. Though errors in the depth-uniform velocity are <2 cm sup>鈭?up> (<10%) at all locations except for the upper continental slope, where apparent but unresolved meander events in water shallower than 500 m can generate depth-uniform errors of order 30%, there are not sufficient observations to confirm these errors directly. Errors in the first order approximation at this location show no non-linear increase due to the joint effect of steep topography and horizontal velocity gradients. Using motional induction in the world鈥檚 oceans, aside from stationary measurements when depth-uniform ocean currents meander across topography, these results suggest that the first order approximation is accurate to within 1-2 cm sup>鈭?up> or less in almost all regions of the ocean, an error similar to the instrumental accuracy of EM instruments.