theubie your tutorial may have some typos in the formula... shouldn't it be:
Abs(Object1.Physics.VelocityX ? Object2.Physics.VelocityX) + Abs(Object1.Physics.VelocityY ? Object2.Physics.VelocityY)
instead of:
Abs(Object1.Physics.VelocityX ? Object1.Physics.VelocityX) + Abs(Object2.PhysicsVelocityY ? Object2.Physics.VelocityY)
Object1 and 2 were mixed up, and there were some . (dots) missing...