The framed ruler is for determining the measurement positon of a wafer on a ellipsometer stage. In our lab the ellipsometer have a free moving stage without any position indicator. By placing the wafer next to the frame and moving the other ruler beam, it it possible to align the laser beam to a centain point.
Acknowledgement to youmaginer jbeale. The original ruler is extended by dulplicating, aligning and cropping. Then two rulers are placed into a frame. Another ruler is printed seperately to be the sliding beam.
Adding a sliding guide is posible, but requires low printing speed. So the slide is not included in the first fast prototyping.