What Is a Synthetic Shift Slot in Capacity Scheduling?

A synthetic shift slot is a placeholder capacity slot the scheduler creates for a date that has no regular shift but is covered by a capacity override. It exists so that hours a planner authorizes on an otherwise non-working day have somewhere to live. In EDGEBIC by User Solutions the slot is labeled as an override day, which distinguishes it from any shift you actually configured.

How it works

Before scheduling any job, the engine builds a capacity map. It walks every work center and every date across the planning horizon, and for each combination where the work center's calendar says a shift is active it creates one capacity slot. The slot records how many hours that shift offers and tracks how many have been consumed as jobs are placed.

The formula behind those hours multiplies the shift's duration by the machine count and the work center's utilization percentage, then subtracts downtime and any partial holiday. Overrides sit above that formula in a priority order: a daily override for a specific work center, shift, and date wins outright; a date-range override is spread across the available days in its window; and the formula applies only when neither exists.

That ordering assumes a slot exists to override. On a day with no active shift, none does. A Saturday on a Monday-to-Friday calendar produces no slot at all, so a planner entering Saturday hours would be entering them into thin air.

The synthetic slot closes that gap. When an override covers a date the calendar treats as non-working, the engine inserts a slot for it, sized at the override's hours and stamped with a placeholder shift identity rather than a real one. From that point the scheduler treats it like any other slot: it searches it, allocates into it, and selects machine instances within it normally.

A concrete example

A machine shop runs one day shift, Monday to Friday. A hot order comes in and the supervisor authorizes Saturday overtime on the mill: eight hours, one crew.

Without a synthetic slot, the planner's only options would be poor ones. Adding a permanent Saturday shift to the mill's calendar would offer Saturday capacity every week thereafter, which is not the intent. Leaving the calendar alone would mean the scheduler simply never sees the overtime and pushes the job to Monday, which is not what the supervisor agreed to.

Instead the planner enters an eight-hour override on the mill for that Saturday. The engine sees an override on a day with no shift, creates a synthetic slot for it labeled as an override day, and the mill has eight schedulable hours that Saturday and only that Saturday. Next weekend the calendar reverts to itself, because nothing about the mill's shift pattern was ever changed.

It is the difference between hiring a crew for one Saturday and rewriting the shop's operating hours. The synthetic slot is the one-Saturday version.

How EDGEBIC uses it

Synthetic slots are created during the capacity build at the start of every scheduling run, so they are transient rather than stored: enter the override, run the schedule, and the slot exists for that run and any run after it while the override stands. The override itself is the persistent record, and it has its own glossary entry in capacity override. The range-based variant is covered in monthly capacity override, and the order in which the two compete with the formula is set out in the capacity override resolution chain.

The practical case, authorizing weekend hours without changing a calendar, is walked through end to end in running a weekend on a capacity override in EDGEBIC. How the underlying figure is derived on a normal day is explained in how capacity is computed for a work center, shift, and day, and the tracker that holds each slot's consumed hours has its own entry in shift resource allocation.

The one thing to remember is that a synthetic slot carries a placeholder shift identity, so any report grouped by shift will show its hours under the override-day label rather than under a named shift. For the wider vocabulary, see the manufacturing glossary, and to see overrides inside a live plan, explore EDGEBIC.