  After having shown that the corresponding components of a four vector
transform via the same transformation factors as the space-time coordinates of
the same event do, we design a relativistic diagram that displays in true
values theirs components. One diagram works for events generated by tardyons
whereas a second diagram works for events generated by light signals or
photons. We consider both approaching and receding tardyons respectively
photons in each case. We also show how the relativistic diagram for radar and
photographic detections of moving profiles.
