Assemble the strips onto the backing manila paper so that they move freely. It's important to have the pins go through the very centers of the first two blue lines. What the students will now do is see how the phase relation of the waves represented on the strips change as the angles of the strips are made to move. Note that you have to keep the strips parallel to make this work. When the strips are aligned parallel and in the direction of the line you drew, this is the zero-order interference direction.
All colors are in phase here.
But, as you move the two strips to other directions, the phase relationship between the two sets of waves change. Draw a line in each direction. Record the wavelength too in the table below. Have the students summarize what's going on in their own words. Now use the real spectrometers.