in other words, what is true is that the entire region above the'x' axis is positive't' and that an event that is. further up than another is later as viewed by this observer and similarly the entire region above in this sense, the x prime axis is at +t prime and the region below it in this direction is at -t prime and the order of the events can be read off from this grid, you draw the grid and if you have some random event over here the infamous birthday party that we spoke of, over here.