Thanks for all the responses! I used this solution and it works like a dream. I went one step further and stored the angle as an instance variable too for easy access.
[QUOTE=Baked] To calculate an objects angle of motion, create 2 instance variables for the object called 'PreviousX' and PreviousY'
at the end of your events add
Every Tick -> Object: Set PreviousX to X
Object: Set PreviousY to Y
Then to calculate the objects actual angle of motion use Angle(Object.PreviousX,Object.PreviousY,Object.X,Object.Y)[/QUOTE]