The term comoving frame is also a good description of a non-inertial frame, which is useful for many of the same uses as we mentioned previously. One advantage of proper frame and comoving frame is that the two frames must always maintain the same spatial position (i. "in the frame" - e.g. on the same frame of reference). This includes that the frame must always be in position in the spacetime frame and thus the spacetime can be viewed as having "no axis". As our first example of a proper frame, one uses the following frame to find the Earth: