The pulsators along and near the main sequence are well-suited for asteroseismology and provide a probe of the stellar interior and its changes with evolution. With the exception of rapidly oscillating Ap stars (roAp), the pulsation periods range from 0.5 h to days. This requires multisite campaigns lasting several weeks. The δ Scuti, roAp and β Cephei variables offer the greatest potential, while the longer-period g-mode pulsators (SPB - slowly pulsating B stars - and γ Doradus variables) are very difficult to study. A summary of the multiperiod structure of δ Scuti stars is given. The two best-studied stars, FG Vir and CD-24°7599, both have been WET targets. A preliminary analysis of the 1995 campaign of FG Vir has already detected 19 frequencies. The standard photometric WET technique has a high duty cycle since the variable star is observed continuously with one channel. The study of main sequence variables requires photometric stability at low frequencies. The extension of the WET technique to low frequencies and its modification are discussed.