Critical Number
Definition
A critical number is the one metric a company or team chooses to move in a given quarter or year — the number that reflects the constraint currently holding the business back. Scaling Up puts exactly one on each horizon of the One-Page Strategic Plan, on the reasoning that a list of priorities with no number attached gives nobody a way to rank them.
It is chosen by finding this period's bottleneck, not by picking the most important metric in general, which is why it often changes from quarter to quarter while ordinary KPIs stay on the dashboard year-round. It is written with a baseline, a target and a date. Harnish pairs it with a counterbalancing number so that the obvious way to hit it does not damage something else: speed paired with quality, growth paired with margin, volume paired with rework.
The usual problem is choosing a number the quarter cannot actually move. A lagging figure in a business with a nine-month sales cycle will finish the period roughly where it started regardless of what anyone does, and the team learns the wrong lesson from a flat line — that focus did not help, rather than that the measurement window was too short.
Example
A 90-person manufacturer set on-time delivery as its critical number: 78% at the start of Q2, target 92% by 30 June, counterbalanced by returns staying under 1.5%. It finished at 89% with returns at 1.2%.
See also: scorecard software