Duplicate track
Work in progress: This section is still a work in progress — content is being added and revised continuously.
What is checked? Whether several pieces of track sit in the same place on top of one another — on the same layer and at the same height. Every connected area where this happens is reported, together with the number of surplus pieces.
Why does it matter? Two pieces in the same place are invisible: the upper one covers the lower one pixel for pixel. They are still counted — in the parts list, in the build plan and in the price. The plan that prompted this rule counted 218 pieces of track in only 72 distinct places: 146 of them were invisible copies. Order from a parts list like that and you buy a multiple of what ends up on the baseboard.
How to fix it: Select the reported area and delete the surplus pieces (the topmost track can be selected on its own; the next one underneath then shows up). Such a stack usually comes from building the same parallel track several times, or from pasting/duplicating twice — neither of which gives you any visible feedback.
Numbers & defaults: A piece counts as coincident when its axis stays within 8 mm (H0, scaled by scale) of the other one over its entire length. Bridges, helixes and a second level are exempt: they differ in height (from 10 mm) or sit on a different layer.