The support/case is completely open in the back, from which a beam that has passed through the grating comes out, while the other side is closed by a thin metal plate on which the main characteristics of the instrument are written:
- number of plates 12;
- plate thickness 10.265 mm;
- step depth 1 mm;
- refraction index for Fraunhofer's line D 1.5086 and its miscellaneousations C-D, D-F and F-G.
It is in a good state of repair.