You can use an amplitude tabulor.
example if u have 1000mm/s
Time/frequency Amplitude
0 0
0.030999828 31 --> d/t = 31/0.03099828 =1000mm/s
0.080999828 81 --> d/t = 81/0.08099982 =1000mm/s
0.130999828 131
0.180999828 181
0.230999828 231
0.280999828 281
...