atChange, the default — one sign where the value changes, and none after it, which is where
the road posts its own. Sections of a sign-posting type tile the route end to end and no two
consecutive ones carry the same value, so every section boundary is a change.along — the sign repeated down the stretch at a fixed screen spacing, so a reader zoomed into
the middle of a long one still sees the value in force. A stretch too short on screen to fit a
sign draws none.A stretch can run 50 km, so under atChange a reader zoomed in past its start sees no sign until
the next change — as on the road itself.
Where a section's signs are posted along the stretch they belong to.