Since its introduction in 2008, NIST DTSA-II has become an important tool for charting the outer limits of the abilities of energy dispersive X-ray spectrometry to make accurate and precise measurements of material composition. With tools for simulating and quantifying electron-excited X-ray spectra, NIST DTSA-II has been used to challenge the primacy of the long-established technique of wavelength dispersive X-ray spectrometry. This challenge has inspired people to rethink the design of the electron microprobe building on the strengths of both the wavelength and energy dispersive X-ray spectrometers to build the next generation instruments which will have both better accuracy and better throughput.