Personally I don't consider that a spectroscope because there is really no way to calibrate it. A drop of water, a prism, a piece of crystal, or anything that has fine equally spaced lines (e.g. a gradient) is capable of separating light into its component wavelengths. Without some means of controlling the incident angle such as a slit that is somehow held at a constant angle with respect whatever is acting like a prism or gradient, you can't control where the spectrum will appear (if at all).The third spectroscope they sugggested is just positioning a CD to where the spectrum is visible on it. Could i just draw the scale onto the CD?
You maybe able to take that idea and make it into a spectroscope by attaching the CD to something that can be used to hold it at a constant angle that also can act as a slit so that the spectrum is always displayed in the same place on the CD surface in which case you can draw the scale onto the CD.