Some Details
         Here are some technical details explaining what's going on inside phat.C, phatic.C, phatset.C & typical user macros for the benefit of those writing user scripts or even making additions and changes to phat.C.

•  There seems to be no alternative to requiring the use of "standard" global names det, data, ev, v1, iev as defined in phat.C in all user macros.  These are used in "common" initialization spanning user macros.
•  Integers rather than booleans are used because they allow expansion to other uses.  Strings may be used eventually for even more flexibility.
• gSystem->ProcessEvents(), introduced in ROOT 2.10, was extremely valuable in allowing an interruptable delay loop for interactive parameter setting without the much more complicated setup involved with the TTimer class.
• Obviously, the "user macros" must be findable so they must be in phat.C's directory or on the search path set by .rootrc
• It seemed easiest to "hard code" button locations in phatic.C by reading coordinates off a gridpaper sketch of the desired GUI rather than getting clever with indexed increments.  These would be useful of course for rows of many identical buttons.
• The button functions call a separate macro, phatset.C.  This avoids the problem of very long command lines within the button definition, a lesson learned from my earlier "toy model" event display demonstration.  The button functions can then occupy many lines, such as for the "GO" button.