The axes of simultaneity are not parallel between the two frames.
Well, no they're not, but they can be figuratively depicted as such insofar as they're relevant in the circumstances discussed here... In the 'real world' the axes would be distorted by the time dilation effect. That was assumed..
200 posted on 06/17/2004 10:09:17 AM PDT by AntiGuv
(When the countdown hits zero - something's gonna happen..)