Attend Fraction Explained: One Operator, Seven Machines

The attend fraction is a routing-step setting that states how much operator attention each machine-hour of a run consumes: 0.0 means the machine runs itself once set up, 0.5 means one person can tend two machines, 1.0 means someone stands at the machine the whole run, and 2.0 means a two-person crew. It is the single number that lets a scheduler tell the difference between a lights-out CNC cell and a hand-fed press, and without it, labor-aware scheduling either oversells people or pretends automation does not exist.

This entry is part of the EDGEBIC glossary; the wider dictionary lives in the manufacturing glossary.

How It Works

Operator-aware scheduling in EDGEBIC by User Solutions runs on an hours ledger: each qualified operator contributes a pool of hours per shift per day, and every scheduled operation draws from that pool. The attend fraction decides the exchange rate, with one fixed rule on top:

Setup always books at 1.0. A person fixtures the machine, loads the program, and proves the first piece regardless of how automated the run is. The fraction only scales the run phase.

Per scheduled slice, the operator cost is: setup hours at full attention, plus remaining run hours times the fraction.

Two consequences of the 0.0 default are deliberate. First, a run with zero attention may legitimately execute on completely unstaffed days: the machine runs itself overnight, which is the entire economics of lights-out machining. Second, a step with setup can never start unstaffed, because the setup needs a human; a skill nobody on the roster holds fails loudly at scheduling time instead of silently pretending. And the default errs on the visible side: a forgotten fraction under-books people, which shows up immediately, rather than silently overselling them.

The Worked Example: One Operator, Seven Machines

From the EDGEBIC documentation. A cell of seven CNC mills, one instance each, on an 8-hour day shift. Every job's step: 1 hour of setup, 9 hours of run, a setup skill required, attend fraction 0.0. Joe is the only qualified operator, with 8 pool hours per day.

• Each job costs Joe exactly 1 hour: 1 setup hour × 1.0 + 9 run hours × 0.0.
• Jobs 1 through 7 all start Monday. Seven machines running; Joe has spent 7 of his 8 hours. The runs continue into the unstaffed evening, because at fraction zero the run phase is unconstrained by people.
• An 8th job's setup still fits Joe's last hour.
• A 9th setup slides to Tuesday. There is no ninth hour of Joe.

One person legitimately launches a seven-machine lights-out cell, and the ledger never claims more of him than exists. Change the fraction to 0.5 and the same 8 pool hours afford 1 + 7 ÷ 0.5 = 15 machine-hours per day; change it to a 2.0 crew with only Joe qualified, and each machine's day caps at (8 − setup) ÷ 2 run hours, so the work splits and slides until a second qualified person joins the roster.

How EDGEBIC Implements It

• Where it lives: on the routing step, next to the required skill. The fraction editor activates only when a skill is set, and free-text entry accepts any non-negative value, so 0.3 or 1.5 are as valid as the standard four.
• How it gates: the engine checks operator availability at the same chokepoint as machine capacity: a day only offers an operation hours that both the machine and the qualified-operator pool can cover, and each day's allocation is clamped to what the pool affords under the fraction. Multi-day jobs spill cleanly: an 8-hour pool against a 12-hour fully attended job books 8 hours Monday and 4 Tuesday, never overselling either day.
• The involvement rule: a step with zero setup and fraction 0.0 has no operator involvement at all, so the constraint is skipped entirely for that step, and the scheduling log records the skip.
• Composition: the fraction stacks with everything else. Machine calendars, holidays, and downtime are checked first; the operator gate asks its question only about days the machine could work. Pinning a named operator to the step narrows the pool to that one person, so their vacation becomes visible schedule slip rather than a silent substitution. Steps routed to a machine pool pick their machine with staffability included, so a fast machine whose shift nobody qualified can cover loses to a slower one that can actually be staffed.
• The optimizer stays honest: jobs carrying operator constraints are locked during mathematical optimization and reproduced exactly as the standard engine scheduled them, so no proposed plan can ever violate a people constraint the model does not represent. Details in the optimizer guide.

The attend fraction is one of several places where EDGEBIC's scheduling engine chooses an hours-based model over a simpler presence flag; the payoff is that plans respect the difference between having a person and having enough of a person.