The 77738 Motor Driven Curved Slit Assembly is used with the MS257 and has 20 mm high slits which are slightly curved to compensate for the inherent bending of the entrance slit image. Slit widths range from 4 μm to 2.0 mm, as with the 77722 Assembly (repeatability and accuracy are also the same as the 77722). The 77738 gives better throughput and better resolution, despite the larger, 20 mm height. Factory recalibration service is recommended when transitioning to a motorized slit assembly.