Kinematics of two fast coronal waves observed with STEREO-A/EUVI (left: 2007 May 19; right: 2009 Dec. 22). The plots show the deprojected distance d of the leading edges of the wavefronts from the extrapolated radiant point (upper half of the plots), and the corresponding speeds v (lower half), both as a function of time t. Also shown are 2nd degree polynomial (black line) and power-law fits (grey line), and the corresponding mean acceleration and the power-law index δ is indicated. To the right of and δ, the reduced chi-squared values for the polynomial and power-law fit is given, respectively. Note the pronounced deceleration of the waves, and the fact that the power-law provides a better fit than the polynomial.