The frequency spectrum in Fig. 1 shows that at least five pulsation modes are excited in DD Lac. Three frequencies, f1, f4, and f3, form an equidistant triplet. In addition to the value of the central frequency, f4, the triplet can be characterized by the mean separation, S = (f3 − f1)/2, and the asymmetry, Δf = f4 − (f1 + f3)/2. Taking the values of the frequencies from a recent analysis of all available data (Pigulski 1994), we get S = 0.15544 ± 0.00021 and Δf = −0.00014 ± 0.00029 d−1.