InputEventScreenDrag - speed

Hi,

In the documentation for InputEventScreenDrag, the property speed is not explained adequately imo. From my testing, if I drag a small distance fast, I get a low number, but if I drag a larger distance slowly, I get a much bigger number. That isn't how I would expect a property representing speed to work, however without any real explanation in the docs as to what exactly speed is supposed to output it's hard to know if this is a bug.