15.64.31.12  NTUPLES   - You  may select the NTUPLE data and put it into a
1-d histogram.  These options remain the same, unless respecified.  If the
option  is  used  without any parameters it is reset to the initial value.
You may show the options by:  SHOW HISTOGRAM SELECT These options are also
used to control NTUPL usage by:  DEFINE HISTOGRAM ADD/SUBTRACT commands
     1.  NTUPLES  selects  only NTUPLES.  Normall NTUPLES are excluded, so
         you must use this option to look at NTUPLE data.
     2.  EVENTS  FROM n1 TO N2 selects the event range The event selection
         remains the same, unless respecified.
     3.  X/DX/Y/DY...NDW=n  selects  the  value  to put into X/DX...  from
         each NTUPLE Initially they are X=1, Y=2,  ...W=6,  DX=-1,  DY=-2,
         DZ=-3.   0  is the event number while positive values are each of
         the variables in an NTUPLE.
     4.  NLIMIT=n  FROM  n1  TO  N2 places limits on the selected value n.
         Where n is the coordinate in the NTUPLE.  If specified without  a
         value  n  or with n=0 then all limits are set.  If all parameters
         are unspecified then all limits are reset to large values.
     5.  NMASK=n Sets MASK number n.  If 0 all masks are cleared.
         A.  IDENT=n Will mask the data by histogram n
         B.  X=m  Specifies  which  Variable  to  check  against  the X of
             histogram n Zero is the event number.
         C.  Y=m  Specifies which Variable to check against Y of histogram
             n
         The   data   is   checked   against  the  histogram  and  if  the
         correspoinding bin of the histogram is  non  zero  the  NTUPL  is
         kept,  and  discarded  if not.  These options are also use by the
         DEFINE HISTOGRAM command to  ADD  or  SUBTRACT  NTUPL  data  from
         histograms.

                                  example
You  have an NTUPLE with 6 coordinate values A,B,C,D,E,F You may place all
of the C values into X and the F values into Y While limiting the B values
to the range -1 to 1.
     TD:SET HIST ID=5 EVENTS X=3 Y=6 NLIMIT=2 FROM -1 TO 1
The resulting data may then be histogrammed using the BIN command.