The ACCM function calculates the magnitude of the second time derivative of the displacement vector of marker i from marker j. The time derivatives are taken in the reference frame of marker l. Markers j and l default to the global coordinate system and the global reference frame if they are not specified.
ACCM(i[,j][,l])
| i | The marker whose acceleration is being measured. |
| j | The marker with respect to which the acceleration is being measured. Set j = 0, while still specifying l, if you want j to default to the global coordinate system. |
| l | The reference frame in which the second time derivative of the displacement vector is taken. Set l = 0 or omit the argument if you want the time derivatives to be calculated in the ground coordinate system (GCS). |
Mathematically, ACCM is calculated as follows:
where 
is the displacement of marker i in ground
and 
is the displacement of marker j in ground.
Note that for any vector quantity 
:
ACCM(21,11)
This function obtains the magnitude of translational acceleration of Marker 21 with respect to Marker 11. Because the l marker is not specified, the derivatives are taken in the inertial reference frame.
ACCM(21,11,32)
This function defines obtains the magnitude of the translational acceleration of Marker 21 with respect to Marker 11. Vector time derivatives taken in reference to Marker 32.