Given a set of end user requirements that establish the overall performance goals of a system, the error budget allows a system architect to seek an optimum balance between various subsystems to achieve the most efficient design. When factors that contribute to the overall error budget are poorly understood the result is likely a suboptimal design that relies on the designer's knowledge of the "art" as opposed to the desired but absent scientific understanding. This typically leads to overengineering of other subsystems to compensate. One factor not strongly quantified is drift due to charging. In this article, the authors explicitly examine contributions due to particle contamination, voids in conductive coatings that expose insulating material, and contamination induced insulating films on conductors in the electron optic subsystem.