User rule (20 Oct 2026, Ostrava bus 21): "You should always size it from the pattern you are suggesting - for all lines." Bus 21 had been sized at 4 from the every-20 timetable around 16:00, plus the tail of buses still on the road, while the sheet suggested every 40, which 2 buses run. The user had found 3 enough in the game.

Why: the owner types the suggested pattern into Simutrans; a need from another pattern is wrong in the game. How to apply: compute the schedule first, then the need by following a vehicle round the suggested slots (real running times, minimum layover); Ostrava's lib.pattern_need does this. Don't add "variant extra" buses for unmodelled variants. When needs drop on a published sheet, mark the extras "not needed (park it)" rather than reshuffling (fewest moves), and show what the slower option would need on rows to check. Related: schedule-both-ends-same-rate, shortest-terminal-wait-rule, city-pipelines