Actual speed of object on curve It is possible find the actual speed of object animated along a curve at a specific frame?

The object has a follow path constraint and it is animated by offset. I'm making a car animation and it would be useful to know this.

I can get the curve's length by Curve Length Add-on it's in the description of this tutorial.
I figured it out, I must measure the distance between one frame and multiply it by (scene fps)*60*60/1000, the result is in km\h (one scene unit is one meter).

An automatic solution would be better though.