When a job is forward-scheduled, it is always placed on the board so as to be scheduled as left as possible,
without regard to its date required. Conversely, a backward-scheduled job is placed on the board , starting with
its last process (in routing order), at its just-in-time position (its date-required in the case of the last process),
moving backwards, up the routing order, toward the now-line.
When backward-scheduling, if PS finds a process already at a position on a resource row that would otherwise
be required for this job, the process will be moved in front of (to the left of) the process already in place, if
possible.
If the now-line is reached before all processes are laid out, the job is deemed to be late and is then forwardscheduled
instead. An alert is raised in this instance.