1338 ‘ v ’ observations were obtained of the δ Scuti variable 1 Mon in 1972/73. Frequency analysis revealed a spectrum with II frequencies of the form nf1 ± mfL, where f1 = 7.346132c/d and fL = 0.12911 c/d. The frequency spectrum was discussed both in terms of the non-linear superposition of waves of frequencies f1−fL, f1 and f1 + fL and in terms of the tidal modulation of a single wave of frequency f1 with a frequency fL. It was concluded that both theories might produce the observed frequencies, but that the most probable cause was the superposition of three non-sinusoidal, interacting waves.