I have a sample set of data similar to the the one depicted in following picture frequency response
I have taken the rate of change for each point in the data set as show below.
(1) $\quad (f_2-f_1)/(t_2-t_1) = df/dt$
What I am actually after is the rate of change of each point relative to the first point $(t_0=0).$
(2) $\quad (f_2-f_0)/(t_2-t_0)$
My problem is that when I plot the second dataset (2) I dont know what to call it . The first equation (1) is a derivative of the dataset but I dont know what the second one (2) should be called.