Top: image of the loop at 94 Å with the curved slit in red. Middle: TD maps from the curved slit. The red data points track the oscillation and are determined by eye. The oscillation in green is obtained by fitting the red points. Bottom: wavelet power spectrum of the oscillation profile. The green continuous line shows indicatively the rate at which the period of the slow wave varies (0.1 min min^-1), while the green dot marks the value of the period (13 min) after 30 min from its excitation.