How do I estimate the derivative of the current position, when I have only values from past to present? If I have a discrete real-time signal $x[n]$, with its latest value $x[i]$ and all its past values $x[i-t]$, how can I estimate the derivative at $x[i]$?
Is the derivative between x[n] and x[n-1] useful enough, hence x'[n] = x[n] - x[n-1] ? Or do you need a better estimate?