How to interpret Event.current.delta?

Hello I'm new to Unity. Right now I'm developing my first game and I'd like to know how to interpret Event.current.delta x and y values. When I have object that moves with cursor on screen I track it's last location and new location to be set in current frame process. I can also calculate it's delta position based on those two values but Event.current.delta gives me some absolute value instead of decimal fraction of the movement in World. Now if I recalculate them like this:

 Vector3 pos = Camera.main.ScreenToWorldPoint(Event.current.delta);

Then I get values that are closer to what I want but still it's above 1 and it should be at about 0.001. I don't want to recalculate this by myself when Event.current.delta is filled by Unity engine but like the question states: How to interpret Event.current.delta to be usable values? I found out that in camera class there are methods with Matrix4x4 and I think that I should use them to get the same value as the one I get from manual delta calculation but I don't really know how. Of course I may be mistaken so then please correct me.

So basically:

 Vector3 pos1 = Camera.main.ScreenToWorldPoint(Event.current.delta);
 pos1.z = 0f;
 Vector3 pos2 = new Vector3(lastPos.x - newPos.x, lastPos.y - newPos.y, 0f);
 
 pos1 != pos2

How to calculate pos1 to be equal pos2 using Event.current.delta ?

Thanks in advance.