vector velocity with framerate

Hello!!. I need help with something. I have the vector forward and I want to calculate it´s velocity. To do that I take the actual forward with its Time.time and the forward vector from last frame(with its Time.time as well). Then I do this:

		var vel:Vector3=(VectorFCamera-transform.forward)/(LastTd-Time.time);

Where VectorFCamera is the forward vector from last frame and LastTd the Time.time.
I set a constant velocity to see what happens:

		transform.Rotate(Blur*Vector3.up, Space.World);

Ok. So what I expect is a constant vector velocity, but what I found is a non uniform vector. The direction is correct but the lenght is not.
I think that it depends on the framerate but thats not possible because am considering with (LastTd-Time.time).

Maybe I am doing something wrong. Anyone knows how to solve this?

Uhm, you rotate the object around it’s pivot, so there is no translation of the pivot. Also you don’t use the physics system to move the object, so calculating Speed inside FixedUpdate makes not much sense and could even lead to other problems.