I posted yesterday post about IIR filters but totally missed the topic which I should have started with. It's about systems responses. I had finally some time to document filters we use in code.
The Unit Step Response [lpsa.swarthmore.edu]
Link directs to the unit step response. There's tab also with the impulse response. All explained with introduction and equations followed by pictures.
Website's name is Linear Physical System Analysis. Recommended to read !