The VY function returns the y-component of the difference between the velocity vector of marker i and the velocity vector of marker j as computed in the coordinate system of marker k. All vector time derivatives are taken in the reference frame of marker l. Marker j defaults to the global coordinate system if it is not specified. Similarly, markers i and j default to the global coordinate system if they are not specified.
VY(i[,j][,k][,l])
| i | The marker whose velocity is being measured. |
| j | The marker with respect to which the velocity is being measured. Set j = 0, while still specifying l, if you want j to default to the global coordinate system. |
| k | The marker in whose coordinate system the velocity vector is being expressed. Set k = 0, while still specifying l, if you want the results to be calculated along the y-axis of the global coordinate system. |
| l | The reference frame in which the first time derivative of the displacement vector is taken. Set l = 0 or omit the argument if you want the time derivatives to be taken in the ground coordinate system (GCS). |
Mathematically, VY is calculated as follows:
where:
is
the displacement of marker i in ground. 
is
the displacement of marker j in ground.
is
the unit vector along the y-axis of marker k. -15*VY(236,168,168,168)