1. The problem statement, all variables and given/known data If "d" is the grating constant, determine the ruling (number of lines/grooves per meter) "D" 2. Relevant equations I have spent hours researching sites that are far too complicated for my understanding of physics. As a result the only relevant equation I could remotely relate to this problem is as follows: N= 1/d 3. The attempt at a solution N= 1/1.6555x10^-6m = a really big number! such as 604,230 grooves/m or lines/m It just doesn't make sense and I'm getting upset! Please, pretty please with a cherry on top, is anyone able to help me? Physics is by far my worst subject but I'm trying!