A specification for a device including a set of concentric cannulas may be discovered to have an actual path different from a desired path, due to interactions between cannulas that effect net curvature of the device. The choice of particular cannulas may be corrected by performing a calculation taking into account curvature affecting properties of the individual cannulas including radius of curvature, elasticity, and moment of inertia. This calculation is preferably performed iteratively starting with a most distal cannula and iterating through the cannulas to the proximal end, accumulating net effect of curvature affecting properties.
