Event Vector: [ sec, m, m, m ] or [sec, light-sec, ..]
00th component of metric tensor : m^2/sec^2.
iith components of metric tensor : 1.
0ith or i0th components of metric tensor: m/sec.
4-velocity: [ 1, m/sec, .. ]
4-momentum; [kg, kg*m/sec, .. ]
4-Force : [ kg/sec, kg*m/sec^2...