Units

GiD_Event_AfterChangeModelUnitSystem: will be raised when user change the current unit system or the declared model length units.
old_system and new_system are the names of the units systems before and after the change respectivelly. They could be empty "" or the same (e.g. changing the model length units)

proc GiD_Event_AfterChangeModelUnitSystem { old_unit_system new_unit_system } {
}