The coordinate axes in each frame are parallel (the x and x ′ axes are parallel, the y and y ′ axes are parallel, and the z and z ′ axes are parallel), remain mutually perpendicular, and relative motion is along the coincident xx′ axes. At t = t ′ = 0, the origins of both coordinate systems are the same, (x, y, z) = (x ′, y ′, z ′) = (0, 0, 0). In other words, the times and positions are coincident at this event. If all these hold, then the coordinate systems are said to be in standard configuration, or synchronized.