- The first 3 options (in colors) are shortcuts. 
- Clear Allwill unlock all controllers. You will get
a warning popup the first time you click this telling you
how to undo it.
 
- Set Allis the default and will re-select all
controllers if you have unlocked some or all.
 
- Enforce Allwill automatically sync the viewpoints on
all of the controllers.
 
- Time lockwill lock the- Indexof each controller if
the underlay has multiple sub-bricks (as in a time series
dataset).
 
- IJK lockwill change the viewpoint locking to match
the “i j k” coordinates of controller rather than the
default setting of matching the “x y z” coordinates. So if
the datasets in different controllers have very different
coordinate systems, this will look a bit random.
 
- The next 3 buttons are actually “radio” buttons so they are
mutually exclusive. They control how the overlay is
thresholded. 
- Free Threshis the default and you can set each
controller with a different threshold.
 
- Lock Vallocks the actual value of the threshold (T or
F or whatever it happens to be).
 
- Lock pVallocks the calculated p-value of the overlay
threshold (I find this more useful).
 
- Lock Rangewill lock the range of values of each
controller’s overlay. This will disable- autoRangefor
all controllers. After you engage this, you can click- autoRangein one controller to have all controllers
match that range.
 
- Lock Pbarwill make all controller overlay color bars
match. Without this selected you can have different colors
for each controller etc..
 
- The rest of the buttons allow you to select which
controllers you want to lock together (A through J, although
I think you can have more controllers than that..?)