I have asked a question about this before but this is a different question. The experiment that my lab partner and I performed used a 360 degree rotating assembly which had the light source (Hydrogen and Sodium) and the telescope at opposite ends while the diffraction grating sat in the middle. The trouble is, I did not know that we were supposed to view the "spectroscopy beams" on each side (left and right). This is the confusion, I have angles (I'll post them here tomorrow when I can access my room in daylight as my roommate is sleeping) but I don't know if I measured left and right. Is it possible to view the first and second order of Hydrogen on one side only? (think a quarter of a circle and you decrease angle). I don't know anything about the machine, I wasn't aware of it at the time but I didn't take into account where the light source was (what angle relative to the whole assembly) and where the scope was... So far I am able to get that the wavelength of the red beam which was at 205 degrees, to be 680nm roughly, I couldn't get a real answer without subtracting 360 by 205 degrees, which I don't know if this makes sense. Did I just get lucky? Other groups who also performed the experiment had angles with a range of 4 to 16 or more but it was a small number compared to 155 degrees. Can someone shed some light on my meagre mind?