Histograms and Ntuples in HBOOK are identified by a positive
or negative integer.
Thus the histogram identifier ID = 0 is illegal at booking time.
However it is a convenient way to specify that the option or operation
applies to all known histograms in the current
working directory (e.g. output, input, printing).
All routines for which a zero identifier is meaningful
are mentioned explicitly.
In agreement with the Fortran standard, when calling an
HBOOK routine the type of each parameter must correspond to
the one described in the routine's calling sequence in this manual.
Unless explicitly stated otherwise, parameters whose names
start with I, J, K, L, M or N are integer,
the rest real, with the exception of those beginning
with the string CH, which correspond to character constants.
All booking commands that reserve space for histograms or plots
require the ``packing'' parameter VMX.
It corresponds to the
estimated maximum population of a single bin,
on the basis of which a suitable number of bits per channel will be
allocated.
This allows several channels to be packed in one machine word,
and thus to require less storage space (at the expense of packing
and unpacking processing time).
A value VMX=0.0 signals that no packing is to be performed
and that each histogram channel will occupy one machine word.