The reference point marker (+) is visible on MPR groups when you activate Swivel mode. The reference point is united with the relate point, even if the relate point is located on a different slice.
When Swivel mode is active, the reference point and relate point move together as you scroll or swivel through an MPR group.
If you activate Swivel mode and then choose and activate a different MPR group, the reference point appears only after you start to manipulate and swivel the group.
Click the reference point marker (+) and drag the marker to a different location. Repositioning the reference point marker will also affect the relate point marker.
When you switch to another mode, the reference point marker is hidden.