Several authors have assumed that the high amplitudes Sct stars do not show changes of amplitude of their light curves in the long term, that is, the light curves of these stars are stable in amplitude. However, at this time, there is not any detailed work in the literature devoted to this aspect. The aim of this work is to analyse the behaviour in the amplitude for monoperiodic high amplitude Sct stars. For any of these variables, there are photometric observations available in the literature over a long time span. For each star, we have analysed all the reliable photometric datasets found in the bibliography in order to find any sign of amplitude variation in the light curves from one year to another.
N d is the number of datasets used for each star.
A comparison was made of the amplitudes obtained for different years. When necessary, the observations collected by the same author, over two consecutive years, were analysed together as only one dataset. Annual mean amplitudes into the Johnson V filter for the sample of stars. Firstly, the data corresponding to each dataset were phased from 0 to 1 using a linear ephemeris with the periods listed in Table 8 . For this, we use or derive one time of light maximum from the corresponding data.