Calculations Step and Delta

Dear Grafana Community,
Does anyone know how the “STEP” and “DELTA” calculations [1] work?
I would like to plot the changes (in absolute value) of one field:
i.e. values:12,16,18,10,6 → plot: 0*,4,2,8,4
I tried to use different transformations but I don’t get this.

  • The first value should be always 0 since it doesn’t have any previous value.

[1] Calculations list | Grafana Labs