The upper slider allows you to simulate a spectrometer sweeping across the relevant frequency range. You will observe a transition, shown by an orange arrow, near the resonance frequency for each transition. No arrows will appear if the frequency is not close to one of the transition frequencies.

The quality of spectrometers is limited by their frequency resolution, which the second slider allows you to vary. At low resolution, the spectral peaks are broadened and the energy levels can be determined with less accuracy. It is the task of the spectroscopist to assign the peaks of the spectrum to specific transitions. If you check the "assignments" box, the results are given.