Coordinate Systems 
Because a difference in position is required when employing the Law of Change for the One-Dimensional Motion with Constant Velocity model, it is important to carefully consider the problem statement, define a useful coordinate system, and accurately assign the initial and final positions. The power to choose an advantagous origin and direction for your coordinates is a feature of all the motion models that can often be exploited to simplify calcuations, but it is important to remember that with great power comes great responsibility: failing to consciously choose a coordinate system can lead to sloppy math and an incorrect solution.