These cursors are simple to use. Just add 'figureC.m' to your path and then call 'figureC' in place of 'figure' in your script. All the rest is taken care of.
Details: A custom figure function ('figureC.m') is used to create a figure which embeds data in the 'UserData' field of the figure. The UserData contains information for a reference cursor. All other cursors are updated with a delta relative to the reference cursor. When the figure is created, the datacursormode 'UpdateFcn' is over-ridden with a custom update function which performs all the delta functionality.
Note: There is a small glitch which sometimes occurs. The reference cursor will have a dX, dY and dZ of 0 instead of the string 'Ref Cursor'. This does not affect functionality. It's just a slight annoyance. The delta cursors will still show the correct values. This is a problem with Matlab not passing in the datacursor obj when it calls the datacursor 'UpdateFcn'.
Resubmitted as .m file instead of .zip