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X-ray scattering by dust is a necessary component of ISM extinction that is not included in typical absorption models for the interstellar medium available in XSPEC e.g. phabs, tbabs, and TBnew. Small angle scattering by ISM dust grains affects any X-ray instrument with sub-arcminute resolution e.g. Chandra, Swift, and XMM. Column densities measured from X-ray obscuration will thereby be overestimated if only an ISM absorption model is used. We simulate a number of Chandra spectra to explore the bias in NH and photon index measurements obtained without inclusion of extinction from dust scattering. We then extrapolate to other observatories, Swift and XMM, whose angular resolution ensures capture of some fraction of the scattered light from dust at intermediate distances between the source and the observer.