The original version of the user manual for the Diffraction Apparatus (DAK), included incorrect values for the spacing of the slits. The error was fixed in the user manual in 2015. At some point, the incorrect values were also posted on our web site. As of April of 2019, the web site has the correct values.

See:
Specifications and User Guide

See also:
Diffraction Apparatus Troubleshooting and FAQs