\chapter{Beams} \section{Starting a beam} Each beam must be declared with a macro issued before the first spacing note under the beam is coded. Two distinct kinds of macros are provided for this. The first kind initiates a ``fixed-slope'' beam, with an arbitrary slope and starting height chosen by the user, while the second kind, a ``semi-automatic'' beam, \ital{computes}~the slope and, in addition, adjusts the starting height in some cases. \def\nps{{\tt\char123}$n${\tt\char125}\pitchp{\tt\char123}$s${\tt\char125}} The basic form of the macros for starting fixed-slope beams is exemplified by the one for a single upper beam, \keyindex{ibu}\nps. Here $n$ is the reference number of the beam, $p$ the starting ``pitch'', and $s$ the slope. The reference number is assigned by the user. It is needed because more than one beam may be open at a time, and it tells \musixtex\ to which beam subsequent beamed notes and other beam specification commands are assigned. By default, the reference number must be in the range [$0,5$], but the range for 8th to 128th beams will be expanded to [$0,8$] or [$0,11$] if \verb|musixadd| or \verb|musixmad| respectively has been \verb|\input|. Alternatively, you can specify the number of $8$th to $64$th beams directly\footnote{$8$th to $64$th beams are so basic that the maximum number of these beams is related to the maximum number of instruments by this command. Using $m>12$ may require e-\TeX.} with \keyindex{setmaxinstruments}\verb|{|$m$\verb|}| within the range $7