Discrete Derivate when an input changes

[GianmarcoSbarra]

Hi, i'm trying to make a discrete derivate. The dt depends on when the input changes and i need to hold the same value of derivate when the input is not changeing.
Right now im trying to derivate a sort of ramp.
The real signal will be a counter who increments when i see something with my webcam, so the dt can change between two counts.
I tried doing like this but doesn't work. 

[Labuser16383]

I am trying to help you. However, i did not find the complete solution up to now.

Part of the solution is to figure out how to display non equal spaced data in the diagram.

I attached an example which does exactly this. I have to combine this with the pointwise derivation code, now. I'm very hopeful to present you the complete solution, soon.

[Labuser16383 · Accepted solution]

So, here it is.

[GianmarcoSbarra]

Thank you!