t u2212 c 1 t since the residue r 1 t still contains information of longer period components it is treated as new data and subjected to the same sifting process this procedure can be repeated on all the subsequent residues and the result is where c k t is the k th imf component and r k t is the residual after extracting the first k imf components the above procedure is repeated to obtain different imfs at different scales until there are less than 2 minima or maxima in a residual which will be assigned as the last imf in one embodiment the received signal may be the ecg signal and is decomposed to a plurality of imfs in fig4 b preferably the ecg signal may be a function of amplitude and time as shown in fig5 the ecg signal is processed with emd eemd to obtain the shape function for modeling the compression signal in another embodiment as shown in fig2 the signal collecting unit 10 may include an ecg port 11 and a reference signal port 12 the signal collecting unit 10 may receive a reference signal which is related with the chest compressions variation of cpr through the reference signal port 12 while receiving the ecg signal an inexpensive accelerometer such as a wrist accelerometer measures the reference signal according to the acceleration generated from the chest compression movement during cpr preferably the reference signal may be a function of amplitude and time as shown in fig6 the reference signal may be processed with.