Finally, as an example of non-inertial observers, assume Candace is accelerating her car. As she passes by him, Alfred measures her acceleration and finds it to be a in the negative x -direction. Assuming Candace's acceleration is constant, what acceleration does Betsy measure? If Betsy's velocity v is constant, she is in an inertial frame of reference, and she will find the acceleration to be the same as Alfred in her frame of reference, a in the negative y -direction. However, if she is accelerating at rate A in the negative y -direction (in other words, slowing down), she will find Candace's acceleration to be a′ = a − A in the negative y -direction—a smaller value than Alfred has measured. Similarly, if she is accelerating at rate A in the positive y -direction (speeding up), she will observe Candace's acceleration as a′ = a + A in the negative y -direction—a larger value than Alfred's measurement.