Mouse distance since pressing button

I need help with my door-open-blueprint. I want drag the door open. I can set the position of a Matinee, but therefor i need to calculate the distance the mouse travelt since i pressed a key. How can i do this?? Or how can i do it in a other way?

Depends what exactly you want to track, if your door opener should be like drag mouse from left to right to certain distance, its quite easy to setup detecting mouse click store location and on mouse release get mouse location again and do little bit of math for distance and drag direction.