Summary plot for one of the analyzed stars. Panel a: original OGLE I-band light curve folded with the period of pulsation, with the corresponding Fourier fit overlaid. Panel b: same as (a), but with the long-term changes removed. Panel c: same as (a), but for the V-band data. Panel d: same as (b), but for the V-band data. Panel e: I-band data after subtraction of the Fourier light-curve model. The orange dots and lines show the fit of the long-term changes in brightness. Panel f: same as (e), but for the V-band light curve. All light-curve points are colored according to the estimated mean-magnitude values during the observations, with lighter and darker points corresponding to brighter and fainter epochs, respectively. Above the panels, the OGLE ID, pulsation period, amplitude (Δ_IDR(I)), and amplitude ratio (r_I, V = A(I)/A(V)) of the mean-magnitude changes are given. The complete set of summary plots is available as online material. (see Data availability paragraph).