The article highlights his work characterizing the groove period error present in commercially-available gratings using the AccuFizH100S interferometer in our lab's metrology facility. Jared measured the "flatness" of diffracted orders produced by a constant-period grating. The slopes, or rate of change, of this measurement in the direction of the grooves indicates how well the grooves are placed on the scale of Angstroms or less -- on about the same scale as the size of an atom! (Not bad for a grating with two-day shipping, eh?)
The article is featured here, and makes for a great read!