1 Secondary_Identifiers

  Instead of the usual single identifier for each plot Mn_Fit has two
  identifiers associated with each plot. This permits significantly
  more flexibility in numbering your histograms and enables you to
  group together histograms which are associated with each other.
  To select a plot with a particular secondary identifier when you are
  asked for a histogram number use the syntax `id&idb'
  (e.g. `10&1' to get histogram 10 which has secondary identifier 1).
  If the secondary identifier is omitted, the default will be used.
  The default can be changed with the `SET IDB' command.
  Any plots read in after this command have the new secondary identifier.

  It is also possible to use a register, parameter, etc. as a histogram
  identifier or secondary identifier.

  You can use the `MN_STORE' and `MN_FETCH' commands to store and
  fetch histograms in Mn_Fit format, that will retain the secondary
  identifiers.

2 Examples

!\begin{enumerate}
!\item
!^
  Example 1:
     If you fit a histogram and want to store the function as a plot, it
     will be given the same primary identifier as the histogram you are
     fitting, but a different secondary identifier so that you know with
     which histogram it is associated.
     For example if you are fitting histogram 10 issue the commands:
     DISPLAY
     FUN PLOT 0
     1 -1

     This will store all the functions you are using in the fit as a
     smooth curve in histogram 10&1.
!\item
!^
  Example 2:
     If you wish to compare Monte Carlo and data histograms, you can
     read in both sets of histograms, giving them different secondary
     identifiers, but they will have the same primary identifiers, so that
     you know which ones to compare and can use the same code to make Monte
     Carlo and data plots. For example:
     SET IDB 10
     FET MONTE.HIS 0
     SET IDB 0
     FET DATA.HIS 0
     PLOT 1&0
     OVER 1&10 2/BLUE

     The Monte Carlo plots will now all have secondary identifier 10, while
     the data have secondary identifier 0.
!\end{enumerate}

