This link explains, in simple terms, the difference between static methods and instance methods,
in particular for a vector class. Its examples with PVector (from processing), essentially show how to use the Vector3d.js class. (FALSE)

https://www.khanacademy.org/computing/computer-programming/programming-natural-simulations/programming-vectors/a/static-functions-vs-instance-methods

- Brian

Note, after much confusion, the PVector examples are different from the way Vector3d is written.
So this post should be disregarded. The classes can be written in different, conflicting ways.