The cnumber indicates in wich window(s) the process is visible. It is only necessary for processes that are intended to visible in a scroll or mode7 window. The default value is 0, wich means that the process is visible in all scroll or mode7 windows. Up to 10 scroll or mode7 windows can be defined, wich are numbered from 0 to 9, wich are enumerated by the predefined constants C_0, C_1, C_2, C_3, C_4, C_5, C_6, C_7, C_8 and C_9.
The cnumbers can be added, and the sum of these indicate the visibility. If there, are for instance 4 scroll windows active, (numbered 0, 1, 2, and 3) and a specific process should only be visible in windows 0 and 2, then you should use:
cnumber = C_0 + C2; // this is 1+4
It is possible to change the value of the cnumber in runtime, wich can be handy in certain situations.