The DM function returns the magnitude of the translational displacement vector from marker j to marker i. Marker j defaults to the global coordinate system if it is not specified. DM is the distance between markers i and j and, by definition, is always non-negative.
DM(i[,j])
| i | The marker whose origin is being measured. |
| j | The marker whose origin is the reference point for the displacement calculation. |
Mathematically, DM is calculated as follows:
where 
is the displacement of marker i in the
global coordinate system and 
is the displacement of marker
j in the global coordinate system.
-30*(DM(21,11)-25)**1.72
This function represents the deformation in a spring. 1.72 is the exponent to which the deformation is raised.