[X = Frequency, Y = MJD, ] 3D light curves of selected 3 mm transitions of C₄H, ¹³CO, and CN in IRC+10216. Each panel also displays the average spectrum through the monitoring (black spectrum in the bottom box [magenta for ¹³CO J = 1–0]), observed minimum (in blue) and maximum (in red) spectra (except for ¹³CO J = 1–0), normalized line area (black dots superimposed on the color-coded 3D light curves [magenta dots for ¹³CO J = 1–0 in the left panel]), and sine function fit to these black dots (thick dashed black curve). The right panel additionally shows the IR Band M light curve (red-blue dashed sinus curve, red upper X-axis) obtained from fitting (Shenavrin et al. 2011) data (shown here as red and blue dots brought from their original observation dates to the MJD range of the figure). Phase delays are also shown.