McPherson’s Model 251MX is easy to use and operates over the 0.5–150 nm range by indexing diffraction gratings. It is optimised for high-energy photons including soft x-ray and extreme UV. The Model 251MX does not scan with point detectors, it works exclusively with microchannel plate intensifiers and/or direct detection CCD array detectors. Regardless of type, the detector is located on a flat focal plane. The diffraction gratings are from holographic masters and their laminar groove profile, that looks like a square wave, results in diffraction efficiency in even orders of light lower than either sawtooth or sinusoidal profiles. This helps keep a high-energy spectrum clean and more easily interpretable—especially at short wavelengths.