The Constant-Velocity motion-law is defined by its Velocity.
In the case of a segment that is a Constant-Velocity motion-law, you can enter only its Start-Position and Start-Velocity. Its End-Position is a function of its Segment-Width.
However, it is often useful to define a Constant-Velocity by its Start Position and End-Position. In this case, you must use the Flexible-Polynomial motion-law.
Flexible-Polynomial : Two Position | Constant-Velocity
Constant-Velocity: 'Conveyor' Motion-Law