Make the assumptions visible.

The calculation, in plain sight.

Effective hours = scheduled hours × utilisation ÷ 100.
Task cycles = effective hours × 3,600 ÷ cycle time.
Annual net benefit = effective hours × avoidable hourly cost + other annual net benefit − operating cost.
Simple payback = installed cost ÷ positive annual net benefit.

Task cycles are theoretical, not accepted output. Utilisation should already account for availability, changeovers and interruptions. Avoidable hourly cost must reflect cash costs actually removable or redeployable value that you explicitly choose to model. Avoid double-counting labour or throughput in “other benefit.” Simple payback excludes tax, financing, discount rates, ramp-up and residual value. If net benefit is zero or negative, no positive payback is shown.