OPS.15.1:4.1 - Choose what the decision needs to measure

Name the subject and the consequence being compared. A customer’s time to an accepted result, a machine’s occupied time and the number of service visits answer different questions even when they concern the same order.

Define membership of the counted population. State when a subject enters and leaves that population. For unfinished orders, choose the arrival and completion events for the service being considered. For a ready queue, include the conditions that make the next operation possible.

Separate unique cases from visits. A return for correction may create another visit to a station while the same customer case remains unfinished. If the case is closed and later reopened, decide whether the receiving question concerns separate episodes or one extended service. Use its operating meaning; do not decide from the number of log rows.

OPS.15 supplies the decision-specific account, and OPS.3 helps identify its subjects. A short statement of the chosen quantity is enough when it removes the ambiguity.