Different inertial grids have different rel-coordinates for events. Here, two grids, Grid 1 and Grid 2, differ by a boost, in which Grid 2 is moving along the x-axis of Grid 1, at a speed β, with -1<β<1. The sign of β indicates if Grid 2 moves in the +x direction, or the -x direction.
Given the rel-coordinates of an event as measured in Grid 1, you use the boost transformation to find the rel-coordinates for the same event, as measured in Grid 2.
The form lets you input multiple events for each of the two separate histories. For example, this input for a history:
-100,-150,100,175generates these two events:
(x,ct)=(-100,-150) (x,ct)=(100,175)These events are joined by a line to make a history. If you entered 3 events, then they would be joined to form a single history as well, and so on. Black dots represent the ticks of a wristwatch. The tick marks stretch out as γ increases.
The units used in this chart aren't specified. It shows values only within a certain range, about +/- 225 or so.