1 MADD
  Syntax: MADD ido&idbo id1[:id1n][&idb1[:idbn1]] id2[:id2n][&idb2[:idbn2]] ...
   where: ido              is the output histogram identifier
          idbo             is the (optional) output secondary identifier
          id1,id2,...      are the input histogram identifiers
          idb1,idb2,...    are the (optional) input secondary identifiers
          id1n,id2n,...    are the upper limits of an (optional) range
          idb1n,idb2n,...  are the upper limits of an (optional) range

  Adds a series of histograms (id1, id2) together to make a new one. To
  specify the secondary identifier, precede it by a `&', otherwise the default
  will be used.  (Use the `SET IDB' command to change the default).

  To add a range of histograms, you can specify a range of primary and/or
  secondary identifiers. For example, `MADD 500&1 300:400&1' will add all
  histograms with primary identifiers 300 to 400 and secondary identifiers 1
  and create histogram 500&1. If you give primary identifier 0, the operation
  will be performed on all plots with the given secondary identifier.

