Because Relations constraints are mathematical, you cannot connect operators that output different results, such as vectors and numbers.
This would be like trying to perform math functions using musical notes, or trying to spell with numbers. Some translation must occur before you can multiply the number 6 by the note B-flat.
Luckily, to save you time converting all of your operators to universals, MotionBuilder translates these into a common language by automatically inserting a converter between the mismatched operators.
When you try to connect two mismatched operators (A), MotionBuilder inserts a translator between them (B).
In the previous figure (A), the Joystick operator, which produces a numeric result, is about to be connected to the Cone model, which requires a vector result. When they are connected (B), a Number to Vector converter appears between them.